What depreciation means, and why it front-loads
Depreciation spreads the cost of a physical asset, a van, a laptop, a machine, over the years it is actually used, rather than treating the whole cost as an expense the day it is bought. The idea it is trying to match is simple: an asset's value to the business is consumed gradually as it wears, ages or becomes outdated, so the expense recorded each year should track that consumption rather than the cash outlay. Four different, widely taught methods do that matching differently. Straight-line spreads the cost evenly, on the assumption that the asset loses value at a steady pace. Declining balance and sum-of-the-years'-digits both front-load the expense, charging more in the early years and less later, on the reasoning that many assets, vehicles and machinery especially, actually lose the most real-world value and usefulness in their first few years, then wear more slowly once the steepest part of that curve is behind them. Units of production ties the expense to how hard the asset actually works each year rather than to time passing at all. This calculator runs the same asset, its cost, its salvage value and its useful life, through all four, so the difference in shape is visible on one chart rather than four separate ones.
Straight-line depreciation
The simplest method by far, and the one most small businesses use for straightforward bookkeeping: the depreciable amount, cost minus salvage value, is divided evenly across every year of the useful life. On the calculator's own defaults, a $50,000 asset with a $5,000 salvage value over 5 years depreciates by exactly $9,000 a year, every year, and the book value falls in a straight line from $50,000 to $5,000. Its main appeal is predictability: the same figure appears on the books every year, which is easy to budget for and easy to check.
Declining balance (including double-declining balance)
Depreciation = Book value at start of year × Rate
Declining balance applies a fixed rate to whatever book value is left at the start of each year, rather than to the original cost, so the charge shrinks every year along with the balance it is calculated on. The factor sets how aggressive the front-loading is: a factor of 2 gives the commonly used "double-declining balance" rate (double the straight-line rate), while 1.5 gives a gentler version sometimes called 150% declining balance. On the calculator's defaults with a 2× factor, the rate works out to 40% (2 ÷ 5 years), and the first three years charge $20,000, then $12,000, then $7,200, exactly double what straight-line would charge in year one and shrinking from there as the balance falls.
Applied mechanically, this rate would eventually push the book value below the salvage value, which is not allowed; an asset cannot be depreciated past what it is expected to still be worth. This calculator handles that by capping each year's charge at whatever is left between the current book value and the salvage value, so the last year or two of the schedule may show a smaller charge than the plain rate would produce, and depreciation simply stops once book value reaches salvage. Some textbooks instead describe switching over to straight-line for the remaining years once that would produce a bigger charge than the declining rate; both conventions are standard and, when the switch point is reached before the life ends, arrive at the same total, this calculator uses the simpler cap because it never needs a separate switch-over test. One consequence worth knowing: at a gentler factor relative to a short life, for example 1.5× over only a few years, the declining rate alone may not fully use up the depreciable amount by the end of the stated life, leaving a small undepreciated balance; the schedule and comparison table below show this honestly rather than forcing a number to zero that the method itself would not produce.
Sum-of-the-years'-digits (SYD)
Depreciation in year t = (Remaining years including year t ÷ SYD) × (Cost − Salvage value)
SYD also front-loads the expense, but through a fraction rather than a shrinking balance. Add up the digits from 1 to the useful life (a 5-year life gives 1+2+3+4+5 = 15, the "sum of the years' digits"), then each year's share of the depreciable amount is its own remaining-years count divided by that sum, counting down. On the calculator's defaults, year one's fraction is 5 ÷ 15 of the $45,000 depreciable amount, or $15,000; year two is 4 ÷ 15, or $12,000; the fractions fall by exactly one-fifteenth of the total each year until the last year takes the smallest share, 1 ÷ 15. Because the fractions are built to add to exactly 1, SYD always reaches the salvage value precisely at the end of the stated life, with no capping needed.
Units of production
Depreciation in a year = Rate per unit × Units produced that year
Unlike the other three, units of production ignores the calendar entirely and ties the expense to actual output, miles driven, hours run, items made, whichever measure suits the asset. Divide the depreciable amount by the total units the asset is expected to produce over its whole life to get a rate per unit, then multiply that rate by however many units it actually produced in a given year. A $45,000 depreciable amount over 100,000 lifetime units gives a rate of $0.45 per unit; produce 20,000 units in a year and that year's charge is $9,000, the same figure straight-line gives over the same 5-year life, because 20,000 units a year for 5 years is exactly the even 100,000-unit split this calculator defaults to. Enter genuinely uneven output instead, a busy first year and a quiet last one, say, and the yearly charges move with it while the total across the life stays the same, so long as the units entered add up to the lifetime total.
Choosing a method for the asset in front of you
None of these four is universally "correct"; each is a genuine, textbook-recognised way of spreading the same cost, and the right pick depends on how the asset actually loses usefulness. Straight-line suits assets that wear steadily and predictably, office furniture, buildings, most fittings, and it is the natural default for simple bookkeeping where a constant figure is easier to plan around. Declining balance and SYD both suit assets that are genuinely more useful, and lose more real value, in their early years, delivery vehicles and much production machinery are the classic examples, where a new vehicle's first few years of service usually matter more to the business than its last few before replacement. Units of production suits assets whose wear tracks output rather than the passage of time: a piece of manufacturing equipment run hard some years and lightly in others, or a vehicle where mileage varies a lot year to year, both depreciate more sensibly against what they actually did than against the calendar.
Reading the schedule, the chart and the comparison table
The schedule table above follows whichever method is currently selected, listing every year's depreciation charge, the running accumulated total, and the book value left afterwards. Switching the method seg swaps that table to the newly selected method's own numbers without touching the asset details. The book-value chart plots all four methods at once, cost to salvage, over the same useful life, so the shape of the front-loading is visible directly: straight-line falls in a perfectly straight line, declining balance curves steeply at first and flattens out, SYD curves more gently, and units of production follows whatever output pattern is entered. The comparison table beneath it lines up each method's first-year charge, total depreciation and ending book value side by side; the totals match across all four (subject to the declining-balance note above), since every method is ultimately spreading the same $45,000 depreciable amount, only the timing differs.
A note on tax depreciation and partial years
This calculator works the plain textbook mathematics behind each method; it is not a tax calculator, and no real tax authority simply lets a business pick any of these four freely for its tax return. In the United States, the Modified Accelerated Cost Recovery System (MACRS) assigns each type of asset to a fixed recovery period with its own prescribed depreciation table, generally built from declining-balance and straight-line switching rules, set out in IRS Publication 946. In the United Kingdom, businesses instead claim capital allowances, principally writing-down allowances at rates HMRC sets for different asset pools, which is a distinct system from accounting depreciation and is not something this tool attempts to reproduce. Real depreciation schedules also often apply a partial-year convention in the year an asset is bought or sold, a half-year convention is common under MACRS, treating the asset as if it were placed in service halfway through its first year, so only half a year's charge is taken; this calculator assumes a full year's depreciation in year one and does not model any partial-year convention. Anyone filing an actual tax return should use the prescribed method and tables for their own jurisdiction, or a qualified adviser, rather than the figures here.
Questions people ask
Why do declining balance and SYD charge more depreciation in the early years?
Both are built on the idea that many assets, vehicles and machinery especially, lose the most real-world usefulness in their first few years and then wear more slowly once that steepest drop is behind them. Declining balance does it by applying a fixed rate to a shrinking book value; SYD does it through a fraction that counts down each year. Straight-line, by contrast, assumes the asset loses value at the same steady pace throughout its life.
Which method should I use for a vehicle versus a piece of machinery?
There is no single rule, but the usual textbook guidance is: use declining balance or SYD when the asset is genuinely more valuable in its early years, a fleet vehicle is the classic case, use straight-line for assets that wear evenly and where a constant figure is easier to plan around, and use units of production when the wear tracks actual output, hours run or items made, rather than the calendar. Machinery can reasonably use any of the three depending on how it is actually used.
What happens when declining balance would take the book value below salvage?
This calculator caps that year's charge so the book value never drops below the salvage value entered, and depreciation stops once it reaches salvage. Some textbooks instead describe switching to straight-line for the remaining years once that would give a bigger charge; both conventions are standard and typically reach the same total, but this calculator uses the simpler cap.
Does this calculator follow tax rules like MACRS or UK capital allowances?
No. It works the plain accounting mathematics behind each method. MACRS in the United States and capital allowances in the United Kingdom are both separate, prescribed systems with their own tables and rates, set out by the IRS and HMRC respectively, and neither is reproduced here. A real tax return should use the correct system for the relevant jurisdiction.
What is a half-year convention, and does this tool use one?
It is a partial-year rule, common under MACRS, that treats an asset as if it went into service halfway through the year it was bought, so only half a year's depreciation is claimed in year one. This calculator does not model it; it assumes a full year's depreciation in year one for every method.
Why do all four methods add up to the same total depreciation?
Because every method is spreading the same depreciable amount, cost minus salvage value, over the same useful life; only the timing of the charge differs between methods, not the total amount depreciated. The exception is a gentle declining-balance factor over a short life, which can leave a small amount undepreciated at the end of the stated life, shown honestly in the comparison table rather than forced to match.
What if the units I enter each year don't add up to the total lifetime units?
The per-unit rate is fixed by the total lifetime units entered, so if the yearly units add up to less than that total, the asset will not be fully depreciated to salvage by the last row shown; if they add up to more, depreciation simply stops once the book value reaches salvage. Either way the schedule reflects exactly what was entered.
This calculator illustrates standard textbook depreciation methods for planning and comparison purposes. It is not accounting or tax advice and does not reproduce any tax authority's prescribed depreciation system, such as MACRS or UK capital allowances. Check with an accountant or the relevant tax authority before using any figure here on a real return or set of accounts.