Straight-Line vs Written-Down Value Depreciation for Equipment

Depreciation turns up in asset registers for two unrelated reasons, and conflating them causes a lot of pointless argument.

Finance needs it for the accounts. Operations needs it to answer exactly one question: is this repair quote sensible given what the thing is currently worth? That's it. That's the entire operational use.

This piece is about the second one. You still have to pick a method your finance team recognises, which in practice means straight-line or written-down value.

Straight-line (SLM)

Straight-line spreads cost evenly across the asset's useful life.

Annual depreciation = (purchase price − salvage value) ÷ useful life in years

A £3,000 instrument with a £300 salvage value and a five-year life depreciates £540 a year, reaching salvage value at the end of year five.

Written-down value (WDV)

Written-down value, also called reducing balance, applies a fixed percentage to whatever the asset is currently worth. The charge is large early and shrinks each year, so the asset never quite reaches zero.

Annual depreciation = opening book value × rate

The same £3,000 instrument at a 40% rate:

Choosing between them

That last row is the one operations actually feels. Under written-down value an asset's book value falls below a typical repair quote much sooner, which will push more decisions towards replacement. Neither answer is wrong; you should just know which bias your method introduces.

What to set on an asset, and once

• Purchase price and date — without these nothing else computes.
• Method — straight-line or written-down value, agreed with finance so the register and the accounts do not diverge.
• Useful life in years for straight-line, or a rate for written-down value.
• Salvage value where the item has a meaningful residual worth at end of life.

Set these at acquisition, by category rather than by item where you can, and book value maintains itself from that point on.

Which method for which equipment

Agree this with finance by category rather than deciding per item, otherwise you'll be making the same decision four hundred times.

These are conventions rather than rules, and your accounting policy wins wherever it differs. The point is consistency within a category, not the precise figure.

Part-year depreciation, which trips people up

An asset bought in October shouldn't absorb a full year of depreciation by December. Conventions vary:

• Pro-rata by month — most accurate, and what most asset systems compute.
• Half-year convention — half a year's charge in the year of acquisition, regardless of month. Common in some jurisdictions.
• Full-year in year of purchase — simplest, and overstates early depreciation.

Use whatever your accounts use. The divergence only matters if the two are reconciled, and they should be.

Salvage value, and why most people set it to zero

Salvage value is what you expect the asset to be worth at the end of its useful life. Under straight-line it is subtracted before the annual charge is worked out, so the asset depreciates to that figure rather than to nothing.

Most organisations set it to zero, for three reasonable reasons: it is genuinely hard to predict years ahead, it is usually small enough not to change any decision, and a non-zero salvage value on an asset you eventually scrap leaves a residual balance somebody has to write off anyway.

Worth setting where there is a real second-hand market — vehicles, specialist instruments, some plant. Not worth the argument otherwise.

What happens at the end of the schedule

An asset that reaches the end of its useful life does not stop existing, and this is where registers quietly go wrong.

The first row catches people out. A fully depreciated item is worth nothing on the books and may be worth a great deal operationally. Removing it from the register because finance has finished with it is how equipment becomes untracked.

Revaluation, briefly

Some jurisdictions and accounting policies allow or require assets to be revalued rather than simply depreciated. If yours does, that is a finance process and the asset register should reflect the outcome rather than attempting to compute it.

The practical rule: the register computes book value from a method finance agreed. Where finance does something more sophisticated, the register takes the figure rather than deriving it, and the two stay reconciled rather than competing.

When book value and market value part company

Book value is an accounting construct. It isn't what the item would fetch, and for some categories the gap is large in both directions.

Specialist instruments often hold resale value far above book. Consumer IT usually falls below it faster than any schedule. For a repair-or-replace decision, book value is the right benchmark because it reflects remaining useful life. For a disposal decision, market value is the right one. Using one where the other belongs produces decisions that look defensible on paper and are wrong.

A caution worth stating plainly

An asset register that computes book value isn't an accounting system. It doesn't post journals, it doesn't handle tax treatment, and it doesn't know about your jurisdiction's rules on rates or pooling.

Its job is to give an operational answer to an operational question — is this repair proportionate — and to export clean figures to whoever does keep the ledger. Treat any divergence between the two as a question for finance rather than a bug.