Depreciation Methods Explained: Straight-Line vs Declining Balance
A clear guide to depreciation methods, comparing straight-line and declining balance with worked examples, plus where units of production and MACRS fit for tax and reporting.
Depreciation is how businesses spread the cost of a long-lived asset across the years it is actually used, rather than expensing the whole amount in the year of purchase. Choosing the right depreciation method affects your reported profit, your tax bill, and the book value of your assets. This guide explains how to calculate depreciation using the most common methods, compares straight line depreciation with declining balance, and clarifies where MACRS fits in for US taxpayers. By the end you will know which depreciation formula to reach for and why.
If you would rather skip the arithmetic, our depreciation calculator handles straight-line, declining balance, and other schedules for you. Still, understanding the logic behind each method helps you choose wisely and explain your numbers to an accountant or lender.
What is depreciation and why it matters
When a company buys equipment, a vehicle, or machinery, that asset delivers value over many years. Accounting principles require matching the expense to the periods that benefit from the asset, so the cost is allocated gradually. This allocation is depreciation. It is a non-cash expense, meaning no money leaves the business each year, yet it reduces taxable income and reflects the asset wearing out.
Three inputs drive every depreciation calculation. The cost basis is the total amount paid to acquire and prepare the asset for use, including shipping and installation. The salvage value, sometimes called residual value, is what you expect the asset to be worth at the end of its life. The useful life is the number of years (or units of production) over which you will depreciate it. The difference between cost basis and salvage value is the depreciable amount.
Straight line depreciation
Straight line depreciation is the simplest and most widely used method. It spreads the depreciable amount evenly across the useful life, so the expense is identical every year. This produces a smooth, predictable schedule that is easy to budget around and easy for outside readers to understand.
The straight line depreciation formula is:
Annual depreciation = (Cost basis − Salvage value) ÷ Useful life
Suppose you buy a machine for $50,000, expect a $5,000 salvage value, and a 10-year useful life. The depreciable amount is $45,000. Divide by 10 years and you get $4,500 of depreciation every year for a decade. After ten years the book value equals the $5,000 salvage value. This evenness is why straight line is the default for financial reporting under both US GAAP and IFRS.
Declining balance depreciation
The declining balance method is an accelerated approach. It records more depreciation in the early years and less later on, which reflects how many assets lose value fastest when they are new. Instead of applying a rate to the depreciable amount, declining balance applies a fixed percentage to the asset's remaining book value each year.
The most common variant is double declining balance, which uses twice the straight-line rate. With a 10-year life, the straight-line rate is 10% per year, so the double declining rate is 20%. Each year you multiply the current book value by 20%.
Annual depreciation = Book value at start of year × (Multiplier ÷ Useful life)
Using the $50,000 machine, the first year's depreciation is $50,000 × 20% = $10,000, more than double the straight-line figure. The second year applies 20% to the new $40,000 book value, giving $8,000, and so on. Salvage value is not subtracted up front; instead you stop depreciating once book value reaches the salvage value. Many businesses switch to straight-line in the final years to fully use up the depreciable amount.
Comparing the two methods side by side
The table below shows the same $50,000 asset with a $5,000 salvage value and 10-year life under straight-line and double declining balance. Notice how declining balance front-loads the expense.
| Year | Straight-line expense | Declining balance expense | Declining book value |
|---|---|---|---|
| 1 | $4,500 | $10,000 | $40,000 |
| 2 | $4,500 | $8,000 | $32,000 |
| 3 | $4,500 | $6,400 | $25,600 |
| 4 | $4,500 | $5,120 | $20,480 |
| 5 | $4,500 | $4,096 | $16,384 |
Both methods eventually depreciate the same total amount; they simply distribute it differently over time. Accelerated depreciation defers tax by reducing taxable income sooner, which improves early cash flow, while straight-line gives a steadier profit picture. You can model either schedule with the depreciation calculator to see the full year-by-year breakdown.
Units of production depreciation
A third approach ties depreciation to actual usage rather than the passage of time. The units of production method is ideal for assets whose wear depends on output, such as a manufacturing press or a delivery truck measured in miles. You first calculate a depreciation rate per unit, then multiply by the units produced each period.
Depreciation per unit = (Cost basis − Salvage value) ÷ Total expected units
If the $45,000 depreciable amount corresponds to 900,000 expected units, the rate is $0.05 per unit. Produce 120,000 units in a year and you record $6,000 of depreciation; a slower year with 60,000 units records only $3,000. This method matches expense to revenue most precisely, but it requires reliable usage tracking and a credible estimate of total lifetime output.
What is MACRS?
MACRS, the Modified Accelerated Cost Recovery System, is the depreciation system required for most business assets on US federal tax returns. It is distinct from the depreciation you might use in financial statements. Rather than letting you choose a useful life, MACRS assigns assets to property classes with set recovery periods, such as 5 years for vehicles and computers or 7 years for office furniture.
MACRS uses built-in IRS percentage tables that combine declining balance with a switch to straight-line, and it applies conventions like the half-year convention, which assumes assets are placed in service at the midpoint of the year. Because of these rules, the first-year deduction differs from a simple declining balance calculation. Salvage value is treated as zero under MACRS, so the entire cost basis is recovered over the recovery period. For tax filing, always use the official IRS tables or consult a tax professional, because the conventions and special allowances change with legislation.
How to choose a depreciation method
For financial reporting, straight-line is usually preferred because of its simplicity and the smooth earnings it produces, which lenders and investors like. For tax purposes in the US, you generally must use MACRS, which is accelerated by design. When a business wants to better match expense to how an asset is actually consumed, declining balance or units of production can give a truer economic picture. Many companies maintain two sets of depreciation schedules, one for book purposes and one for tax, precisely because the goals differ.
Consider how to calculate depreciation in the context of your cash flow needs too. Accelerated methods reduce taxable income sooner, freeing up cash early in an asset's life, which can be valuable for a growing business reinvesting heavily. A stable, mature company may prefer the predictability of straight-line. Whatever you choose, the depreciation calculator lets you compare the schedules before you commit.
Common mistakes in depreciation
A frequent error is forgetting to include installation, delivery, and setup costs in the cost basis; these belong in the depreciable amount. Another is ignoring salvage value in straight-line calculations, which overstates the annual expense. With declining balance, people often forget to stop at the salvage value floor or fail to switch to straight-line at the right time, leaving the asset incompletely depreciated. Finally, mixing up book depreciation with tax depreciation leads to inaccurate filings; remember that MACRS rules override your chosen book method for the IRS.
Sum-of-the-years'-digits depreciation
Beyond straight line and declining balance lies another accelerated method worth knowing: sum-of-the-years'-digits, often abbreviated SYD. Like declining balance, it loads more depreciation into the early years of an asset's life, but it does so through a fraction rather than a fixed rate, which gives a smoother taper and always finishes exactly at the salvage value.
The method works in two steps. First, add up the digits of the asset's useful life. For a five-year asset, that is 5 + 4 + 3 + 2 + 1, which equals 15. Second, in each year apply a fraction whose numerator is the remaining life at the start of that year and whose denominator is that sum of 15. The first year uses 5/15, the second 4/15, and so on down to 1/15 in the final year. Each fraction is applied to the depreciable base, which is cost minus salvage value.
| Year | Fraction | Depreciation on a £10,000 asset (£1,000 salvage) |
|---|---|---|
| 1 | 5/15 | £3,000 |
| 2 | 4/15 | £2,400 |
| 3 | 3/15 | £1,800 |
| 4 | 2/15 | £1,200 |
| 5 | 1/15 | £600 |
The depreciable base here is £9,000, and the five fractions sum to exactly that. SYD suits assets that lose value or productivity steadily but front-loaded, such as vehicles and some machinery, and it pairs neatly with our depreciation calculator when you want to compare its schedule against straight line.
Book depreciation vs tax depreciation
One of the most confusing aspects of depreciation for newcomers is that a single asset often carries two different depreciation schedules at once. Book depreciation appears in the financial statements you show investors and managers, and it aims to match the asset's cost to the revenue it helps generate. Tax depreciation follows the rules of the tax authority and aims to determine taxable income, which may deliberately differ.
The two diverge because their goals differ. Accounting standards favour a method that fairly represents economic reality, often straight line. Tax codes, by contrast, frequently allow accelerated write-offs to encourage investment, so a company might claim large deductions early for tax while reporting smooth, even expense to shareholders. The gap between the two creates what accountants call a deferred tax liability or asset, a balance that unwinds over the asset's life.
- Book purpose: present a true and fair view of profit to owners and lenders.
- Tax purpose: comply with statute and optimise the timing of deductions.
- Result: the same machine can show £2,000 of book depreciation and £3,500 of tax depreciation in the same year.
This is entirely normal and legal. The key is to keep two clean schedules and never let a tax figure leak into the financial accounts or vice versa, because that mismatch is a common audit finding.
Depreciation in the US vs the UK
Depreciation rules diverge sharply across the Atlantic, and a method that is standard in one country may not even exist in the other for tax purposes. Anyone operating in both markets must keep the systems separate.
In the United States, businesses depreciate fixed assets for tax under MACRS, a prescribed system of rates and recovery periods. The financial statements, however, follow US GAAP and typically use straight line or an accelerated book method, so American firms routinely run book and MACRS schedules in parallel.
In the United Kingdom, the picture is different in name and mechanism. For accounting, UK companies depreciate assets in the accounts much as elsewhere. But for tax, the UK does not allow ordinary depreciation as a deduction at all. Instead it uses capital allowances, a separate statutory system. The Annual Investment Allowance lets businesses write off a large amount of qualifying plant and machinery in the year of purchase, while writing-down allowances spread the rest at set percentages on a reducing-balance basis.
| Aspect | United States | United Kingdom |
|---|---|---|
| Tax mechanism | MACRS depreciation | Capital allowances |
| Immediate write-off | Section 179 / bonus | Annual Investment Allowance |
| Accounts method | GAAP depreciation | Accounting depreciation, added back for tax |
| Reducing balance | Common under MACRS | Writing-down allowances |
The practical takeaway is that "depreciation" in a UK tax return is replaced by capital allowances, and the accounting depreciation is added back before allowances are applied. Confusing the two systems is one of the fastest ways to file an incorrect return.
Partial-year and mid-month conventions
Assets rarely arrive on the first day of a financial year, which raises the question of how much depreciation to claim in the year of purchase and the year of disposal. Accountants solve this with conventions, standard rules that assign a deemed in-service date so you do not have to track the exact day.
The half-year convention treats every asset as if it were placed in service halfway through the year, granting six months of depreciation in year one regardless of the actual purchase date. The mid-month convention, used for US real estate, assumes the asset went into service in the middle of the month it was acquired. A mid-quarter convention applies when a large share of assets are bought late in the year, preventing businesses from claiming a full half-year on a December purchase.
- Under the half-year convention, a five-year straight-line schedule actually spans six tax years, with half-amounts at each end.
- Conventions affect timing only; the total depreciation over the asset's life is unchanged.
- Choosing or being assigned the wrong convention shifts deductions between years and can trigger penalties if it understates taxable income.
For everyday accounting outside strict tax rules, a simple pro-rata approach by month is common: an asset bought at the start of the ninth month earns four-twelfths of a year's depreciation. The convention you use should be consistent and documented.
Recording depreciation: journal entries and the balance sheet
Knowing how to calculate depreciation is only half the job; you also need to record it correctly so the financial statements stay coherent. Depreciation is a non-cash expense, meaning it reduces reported profit without any money leaving the bank.
Each period you make a journal entry that debits depreciation expense, which lowers profit on the income statement, and credits a contra-asset account called accumulated depreciation. The accumulated depreciation account grows over time and sits on the balance sheet directly beneath the asset, reducing its carrying value, also called net book value. The original cost stays on the books unchanged; it is the accumulated depreciation that climbs.
| Balance sheet line | Year 1 | Year 2 | Year 3 |
|---|---|---|---|
| Asset at cost | £10,000 | £10,000 | £10,000 |
| Less accumulated depreciation | (£3,000) | (£5,400) | (£7,200) |
| Carrying value | £7,000 | £4,600 | £2,800 |
When the asset is eventually sold, you compare the sale price to its carrying value. Selling above carrying value produces a gain; selling below produces a loss. Both are recorded separately from depreciation. Keeping the cost, accumulated depreciation and carrying value cleanly separated is what lets auditors and managers trust the numbers, and it ensures the depreciation you calculated actually flows through to an accurate balance sheet.
Depreciation vs amortisation vs depletion
Depreciation belongs to a family of three accounting techniques that all spread a cost over time, and using the right term matters because each applies to a different kind of asset. They share the same logic but differ in what they measure.
Depreciation applies to tangible fixed assets you can touch, such as machinery, vehicles and buildings. Amortisation applies to intangible assets such as patents, software licences, trademarks and goodwill, spreading their cost across their useful or legal life. Depletion applies to natural resources such as oil reserves, mineral deposits and timber, allocating cost as the resource is physically extracted.
| Technique | Asset type | Examples | Driver |
|---|---|---|---|
| Depreciation | Tangible fixed | Machines, vehicles | Time or usage |
| Amortisation | Intangible | Patents, software | Useful or legal life |
| Depletion | Natural resource | Oil, timber, ore | Units extracted |
One key difference is that land is never depreciated, because it does not wear out or get used up. When a business buys property, it must split the purchase between the building, which depreciates, and the land, which does not. Mislabelling amortisation as depreciation, or depreciating land, are classic errors that distort both the accounts and the tax position.
Impairment: when an asset loses value suddenly
Depreciation assumes a steady, predictable decline, but assets sometimes lose value abruptly because of damage, obsolescence or a collapse in demand. This is where impairment comes in, a separate accounting event that recognises an unexpected drop in an asset's recoverable value below its carrying value.
Suppose a specialised machine with a carrying value of £40,000 is rendered obsolete overnight by a new technology, and its realistic recoverable amount falls to £15,000. Depreciation alone would never capture this; instead the business records a £25,000 impairment loss, writing the asset down immediately. From that point, future depreciation is recalculated on the new, lower carrying value over the remaining life.
- Triggers for impairment include physical damage, technological obsolescence, falling market prices and legal or regulatory changes.
- Impairment is a separate charge from depreciation and is recorded as a distinct expense, often disclosed prominently.
- Under some standards impairments can reverse if conditions improve, while under others they generally cannot, so the applicable framework matters.
Understanding impairment rounds out the depreciation picture: routine wear is handled by your chosen method and schedule, while sudden value loss is handled by an impairment write-down. Together they keep the asset's carrying value honest, which is the entire purpose of depreciation accounting.
Depreciation and cash flow: a non-cash expense explained
One of the most misunderstood features of depreciation is that it is a non-cash expense. When you record depreciation, no money actually leaves your bank account that period. The cash left the business earlier, when you bought the asset. Depreciation simply spreads that already-spent cash across the years the asset earns its keep, so the profit figure on your income statement reflects the true cost of using the asset rather than the lump payment.
This distinction matters enormously for cash flow analysis. Because depreciation reduces reported profit without reducing cash, it is added back at the top of a cash flow statement prepared by the indirect method. A business can show a modest accounting profit yet hold plenty of cash precisely because a large slice of its expenses are non-cash depreciation charges. Conversely, a company can look profitable while quietly running short of the cash it will eventually need to replace those worn-out assets.
- Profit impact: depreciation lowers taxable and reported profit each period.
- Cash impact: none in the period recorded; the cash outflow happened at purchase.
- Replacement risk: because no cash is set aside automatically, prudent owners earmark funds to replace ageing assets.
Understanding depreciation as a timing device rather than a cash movement is the key to reading financial statements with confidence. It explains why two firms with identical cash positions can report very different profits, and why analysts often look at earnings before interest, tax, depreciation and amortisation to strip the effect out.
Depreciation recapture: the tax sting when you sell
Depreciation feels like a gift while you own an asset because it lowers your taxable income year after year. But tax authorities expect to recover some of that benefit if you later sell the asset for more than its written-down value. This recovery is called depreciation recapture, and it catches many small business owners by surprise at the moment of sale.
The logic is straightforward. Suppose you bought equipment for a sum, claimed deductions that reduced its book value to a fraction of the original cost, then sold it for more than that reduced value. The portion of the sale price that simply reverses the depreciation you previously claimed is treated, in many jurisdictions, as ordinary income rather than as a lower-taxed capital gain. In effect, the tax you deferred during ownership is now partly clawed back.
| Item | Amount |
|---|---|
| Original cost | 10,000 |
| Accumulated depreciation claimed | 6,000 |
| Written-down book value | 4,000 |
| Sale price | 7,000 |
| Gain subject to recapture | 3,000 |
In the example above, the gain above book value reverses part of the depreciation already deducted, so it is recaptured. Anything received above the original cost would usually be treated as a separate capital gain. Rules differ between the US and the UK and between asset classes, so the specific numbers vary, but the principle is universal: depreciation is a deferral of tax, not always a permanent saving. Factoring potential recapture into your planning prevents an unwelcome bill when you finally dispose of an asset.
Component depreciation: breaking an asset into parts
Most people picture depreciation applying to a single, whole asset, such as one delivery van or one machine. But many large assets are really collections of components that wear out at very different speeds. A commercial building, for instance, contains a structural shell that may last sixty years, a roof that lasts twenty, lifts that last fifteen and carpets that last seven. Treating all of that as one asset with one useful life overstates the value of the short-lived parts and understates the depreciation in the early years.
Component depreciation, sometimes called componentisation, addresses this by splitting a complex asset into its major parts and depreciating each over its own useful life. It produces a more faithful picture of how value is consumed and matches expenses more accurately to the periods that benefit. It is required under several international accounting frameworks for significant components and is widely used for property, aircraft and heavy plant.
- Identify the major components whose cost is significant relative to the whole asset.
- Allocate the total purchase price across those components on a reasonable basis.
- Assign each component its own useful life and depreciation method.
- Depreciate each separately, replacing and re-capitalising components as they wear out.
The practical payoff is twofold. First, your financial statements reflect reality more closely, which matters for valuation and lending decisions. Second, when you replace a single component, such as re-roofing a building, you can remove the old component's remaining value cleanly rather than awkwardly adjusting one giant asset. To see how different useful lives change the annual charge, drop each component into a depreciation calculator and compare the schedules side by side.
Frequently asked questions
What is the straight line depreciation formula?
Straight line depreciation equals the cost basis minus the salvage value, divided by the useful life in years. For a $50,000 asset with a $5,000 salvage value and a 10-year life, the annual depreciation is $45,000 divided by 10, or $4,500 every year.
How is declining balance different from straight-line?
Declining balance is accelerated, recording larger expenses in early years by applying a fixed rate to the shrinking book value. Straight-line spreads the cost evenly across every year. Both depreciate the same total amount but on different timelines.
Is MACRS the same as declining balance?
MACRS uses declining balance principles but adds IRS-mandated property classes, recovery periods, and conventions like the half-year rule. It also treats salvage value as zero. MACRS is required for US tax filing, whereas plain declining balance is a general accounting method.
Which depreciation method should a small business use?
For internal books and financial statements, straight-line is simple and widely accepted. For US tax returns, you generally must use MACRS. Many businesses keep both schedules because the methods serve different reporting goals.
Does depreciation reduce my taxes?
Yes. Depreciation is a deductible non-cash expense that lowers taxable income, which reduces the taxes you owe. Accelerated methods like declining balance and MACRS shift more of that deduction into the early years of an asset's life.
How do I calculate depreciation on a vehicle?
Start with the vehicle's full cost including taxes and fees, subtract the expected salvage value, and divide by the useful life for straight-line, or apply MACRS tables for US taxes where vehicles are typically 5-year property. Our depreciation calculator can produce the full schedule for either approach.