You bought a van for £40,000 three years ago. It still runs perfectly, delivers your stock every day, and would probably sell for somewhere between £18,000 and £22,000 if you put it on the market tomorrow. So why does your balance sheet say it is only worth £15,000? If you have ever stared at your fixed asset note and wondered whether your accountant has made a mistake, you are not alone. This confusion trips up SME owners constantly, and it can lead to bad decisions — underestimating how much the business is really worth, misjudging when to replace equipment, or panicking unnecessarily when a lender asks about asset values. Understanding net book value removes that confusion and lets you read your own balance sheet with confidence.
What Net Book Value Actually Means
Net book value (often shortened to NBV) is simply the original cost of an asset, minus all the depreciation and any impairment losses that have been charged against it so far. It is an accounting figure, not a valuation. Nobody has gone out and appraised your van — the £15,000 figure is purely the result of a spreading calculation that shares the cost of the van across the years it is expected to be useful to the business.
Here is the key idea: when you buy a van for £40,000, you have not really ‘spent’ £40,000 in the year you bought it, at least not from an accounting perspective. You have exchanged cash for something that will help you earn revenue over several years — maybe four, five, or more. Charging the full £40,000 as an expense in year one would make that one year look artificially unprofitable, and every year after that look artificially profitable, because the van is still being used without any cost being recorded against it. Depreciation fixes this mismatch by spreading the cost over the asset’s useful life, so each year’s accounts reflect a fair share of the cost alongside the revenue the van helped generate.
How Depreciation Gets Us From £40,000 to £15,000
To calculate depreciation you need three pieces of information: the cost of the asset, its estimated useful life, and its estimated residual value (what you think it will be worth, or could be sold for, once the business has finished using it). For our delivery van, let us say the business estimates a useful life of four years and a residual value of £6,667 at the end of that period — a realistic trade-in or scrap value for a van that age.
Using the straight-line method, which is the most common approach for vehicles and most SME equipment, the calculation spreads the depreciable amount (cost minus residual value) evenly across the useful life. The depreciable amount here is £40,000 minus £6,667, which equals £33,333. Divide that by four years and you get annual depreciation of roughly £8,333, with a small rounding adjustment in the final year so the numbers tie out exactly.
| Cost of the van | £40,000 |
| Less: estimated residual value | £6,667 |
| Depreciable amount | £33,333 |
| Useful life | 4 years |
| Annual depreciation charge (approx.) | £8,333 |
Run that annual charge forward for three years and you can see exactly how the van’s book value falls from £40,000 to £15,000 — not because the van has lost that much real-world value, but because the accounts are systematically recognising the cost of using it.
| Year end | Annual depreciation | Accumulated depreciation | Net book value |
|---|---|---|---|
| Year 0 (purchase) | — | £0 | £40,000 |
| Year 1 | £8,333 | £8,333 | £31,667 |
| Year 2 | £8,333 | £16,666 | £23,334 |
| Year 3 | £8,334 | £25,000 | £15,000 |
| Year 4 | £8,333 | £33,333 | £6,667 |
| Account | Dr | Cr |
|---|---|---|
| Depreciation expense | £8,334 | |
| Accumulated depreciation — Motor vehicles | £8,334 |
Year 3 depreciation charge on the delivery van, posted at the financial year end. This entry reduces profit for the year and builds up the accumulated depreciation balance, which is deducted from the van’s original cost on the balance sheet to arrive at net book value of £15,000.
Net book value is an accounting allocation, not a valuation. It tells you how much of the asset’s cost has not yet been charged to profit — it does not tell you what the van is actually worth if you tried to sell it today.
Do not confuse net book value with market value, insurance value, or tax written-down value. For UK tax purposes, vans typically qualify for capital allowances — often the Annual Investment Allowance, which can let you deduct the full £40,000 against taxable profit in year one. That capital allowance schedule is entirely separate from the depreciation schedule in your statutory accounts, so your tax computation and your balance sheet will show different figures for the same van. If you quote net book value to a lender or buyer as if it were the resale price, you risk under- or over-stating what the business is worth.
Why This Matters for Your Business
Net book value affects more than just how a single van looks on paper. It feeds into your total fixed assets figure, which lenders use when assessing security for a loan, it affects the depreciation charge that reduces your reported profit each year, and it influences decisions about when to replace equipment. If a machine’s net book value has fallen to near zero but it is still working hard and generating revenue, that is actually a good sign — the cost has been fully recovered through the accounts, and any further use is effectively free in accounting terms, even though you will still need cash to replace it eventually. Conversely, if an asset still carries a high net book value but has actually broken down or become obsolete, you may need to recognise an impairment — an additional write-down beyond normal depreciation — rather than letting an unrealistic figure sit on the balance sheet.
For finance managers preparing management accounts, getting the useful life and residual value assumptions right matters just as much as the arithmetic. Too short a useful life front-loads costs and understates early profits; too long a life understates depreciation and can leave a nasty surprise — or an impairment charge — when the asset eventually needs replacing well before it is fully written down.
- Check the useful life and residual value assumptions behind your fixed asset register at least once a year — if a van now realistically only lasts three years instead of five, the depreciation charge needs updating.
- When reading a balance sheet, treat net book value as a cost-allocation figure, not a market valuation — ask separately for a fair value estimate if you need to know what an asset could actually sell for.
- Keep a clear separation in your own mind, and in conversations with lenders or buyers, between accounting depreciation (which affects the balance sheet and profit) and capital allowances (which affect your tax bill) — they rarely move at the same pace.
- If an asset’s net book value no longer reflects its true condition or usefulness, flag it to your accountant for a possible impairment review rather than letting the figure drift unchallenged.
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