Straight-Line vs Declining-Balance Depreciation

The total is fixed before you choose

Depreciation spreads the cost of an asset over the periods that benefit from it. What it can never do is change how much that cost was. An asset bought for $50,000 and eventually worth nothing will be charged to profit as exactly $50,000, whatever schedule you use to get there. Straight line does it in five equal slices of $10,000. Double declining balance front-loads it: $20,000, $12,000, $7,200, then $5,400 and $5,400 once the schedule switches. Add either column up and the answer is $50,000. The choice is a choice about which year the expense lands in, and about nothing else.

The two methods answer different questions about the asset. Straight line assumes the asset delivers the same service every year, which fits a building, a fitted-out office, or a licence with a fixed term. Declining balance assumes it delivers more early on, which fits a vehicle, a laptop fleet or any equipment whose repair costs climb as it ages — under declining balance, the total of depreciation plus maintenance stays roughly level across the asset's life, which is often a fairer picture of what the year actually cost. Both are estimates. Neither is more true than the other, which is why standards let you pick the one that reflects the pattern in which you consume the asset.

The schedule, year by year

Double declining balance takes twice the straight-line rate — over five years that is 2 ÷ 5, or 40% — and applies it to the book value at the start of each year rather than to the original cost. Year one: 40% of $50,000 is $20,000, leaving a book value of $30,000. Year two: 40% of $30,000 is $12,000, leaving $18,000. Year three: 40% of $18,000 is $7,200, leaving $10,800. Notice that the charge shrinks every year by construction, because the base it is applied to shrinks. Residual value does not enter the calculation at all; it only sets a floor the book value must not fall below.

Two moments in that schedule are worth naming, because they are often confused. The crossover is the year the annual charge falls below the straight-line charge: here it is year three, when $7,200 drops under $10,000. The cumulative position is different — declining balance is still ahead in total by $9,200 at the end of year three, having been ahead by $12,000 at the end of year two, which is the widest the gap ever gets. From year three onwards the advantage is being paid back, and by the end of year five it is exactly zero. Accelerated depreciation is a curve that starts high, crosses, and returns to the same finish line.

Why declining balance needs a switch, and never reaches zero on its own

Multiplying a number by 0.6 over and over never produces zero. After five years the book value of a $50,000 asset depreciated at a pure 40% would still be $3,888; after ten years $302.33; after twenty years $1.83. It approaches zero and never arrives, which is fine as geometry and useless as accounting — you need the asset fully written off by the end of its useful life. Something has to close the gap, and there are two standard ways: switch to straight line partway through, or write off whatever is left in the final year.

The switch convention is the tidier one, and it is mechanical. In each year you compare the declining-balance charge with what you would get by spreading the remaining book value evenly over the remaining life, and you take whichever is larger. In the worked schedule the test fails for three years — 40% of $50,000 beats $50,000 ÷ 5, and so on — and then fires in year four: 40% of $10,800 is $4,320, but $10,800 spread over the last two years is $5,400. From that point the schedule is straight line, and it lands exactly on zero. The United States builds this into its MACRS tables, where five-year property depreciates at 20.00%, 32.00%, 19.20%, 11.52%, 11.52% and 5.76% of original cost — percentages that already contain both the switch and a half-year convention for the year of purchase, and that sum to 100%.

The economic case is the present value of the tax deferral

Depreciation is a deductible expense, so every euro of it saves you the tax rate in tax. At 25%, the $50,000 of total depreciation shields $12,500 of tax — and it shields exactly $12,500 under both methods, because both deduct exactly $50,000. Anyone who tells you accelerated depreciation reduces tax over the life of an asset is wrong. What changes is when the shield arrives. Straight line delivers $2,500 a year for five years. Declining balance delivers $5,000, $3,000, $1,800, $1,350 and $1,350.

Discount those two streams and you get the number that matters. At 8%, with each year's shield received at the end of the year, straight line is worth $9,981.78 in today's money and declining balance is worth $10,541.62. The difference is $559.85 — 1.12% of the asset's cost, and 4.5% of the tax shield itself. That is the whole prize. It is real and it is worth taking, but it is not the transformative saving accelerated depreciation is sometimes sold as. Whether it is worth any complexity in your books depends on how large your capital spending is and on what money costs you.

The advantage scales with the two things you would expect. Drop the discount rate to 4% and it falls to $315.59, because deferral is worth less when money is cheap; raise it to 12% and it rises to $749.11. Raise the tax rate from 25% to 30% and it rises to $671.82, because a bigger shield deferred is a bigger prize. Both sensitivities point the same way: accelerated depreciation is worth most to a heavily taxed company with an expensive balance sheet, and worth very little to a low-tax, cash-rich one.

What the choice does to the rest of your accounts

Front-loading depreciation depresses reported profit in the early years and flatters it later. In the worked schedule, operating profit under declining balance is $10,000 lower in year one and $4,600 higher in years four and five, on nothing but a policy choice. It also depresses the carrying value of the asset faster, which raises asset turnover — revenue divided by assets — for reasons that have nothing to do with using the assets better. An older asset base depreciated aggressively can make a business look far more capital-efficient than a competitor who bought the same machines last year and uses straight line.

Two practical consequences follow. First, when you compare companies on operating profit, on return on assets or on asset turnover, check the depreciation policy and the age of the asset base before you conclude anything — you may be measuring an accounting convention and a purchase date. Second, in many jurisdictions the depreciation in your published accounts and the depreciation in your tax computation are two different schedules, computed under two different sets of rules, with a deferred tax balance reconciling them. If that is your situation, the accounting method you choose does not by itself determine the tax deferral discussed above; the tax rules do.

Frequently asked questions

Does accelerated depreciation reduce the total tax I pay?

No. Over the life of the asset both methods deduct exactly the same $50,000, so at a 25% rate both shield exactly $12,500 of tax. What accelerated depreciation changes is timing: you get $5,000 of shield in year one instead of $2,500, and correspondingly less later. The benefit is the time value of that shift — $559.85 discounted at 8% on this asset, or 1.12% of its cost. Real, but a deferral rather than a saving.

In which year does declining balance fall below straight line?

On this five-year asset the annual charge crosses in year three: $7,200 against $10,000. Do not confuse that with the cumulative position, which stays in declining balance's favour until the very end — the cumulative gap peaks at $12,000 after year two, is still $9,200 after year three, falls to $4,600 after year four and reaches zero after year five. The crossover tells you when the yearly expense starts hurting; the cumulative gap tells you how much benefit is still outstanding.

Why does declining balance need to switch to straight line?

Because a constant percentage of a shrinking balance is a geometric series that approaches zero without ever reaching it. A $50,000 asset at a pure 40% rate still has a book value of $3,888 after five years, $302.33 after ten and $1.83 after twenty. The switch test — take the declining-balance charge or the remaining book value spread evenly over the remaining life, whichever is larger — closes the schedule exactly on time. Here it fires in year four, where $10,800 over two years gives $5,400 against a declining-balance charge of $4,320.

How does residual value fit into declining balance?

It is a floor, not an input. Straight line subtracts residual value before dividing by the life; declining balance applies its rate to the full book value and simply stops once the book value reaches the residual. That is why the two methods look so different in the first year even on the same asset. In the worked example residual value is zero, so the schedule runs to zero. Give the same asset a $5,000 residual and the final year's charge is capped so that the book value lands on $5,000 rather than continuing down.

Can I use one method in my accounts and another for tax?

In many jurisdictions, yes — and it is the norm rather than the exception. Accounting standards ask you to depreciate over the asset's useful life in the pattern in which you consume its benefits, while tax law prescribes its own rates, classes and conventions. The two schedules then diverge, and the difference is carried as deferred tax. Because the rules differ so widely by country, treat the present-value figures in this article as an illustration of the mechanism, not as your entitlement, and check your local capital-allowance regime.