Depreciation is the systematic reduction in value of a tangible asset over its useful life. It lets you spread the cost of a long-lived asset (a vehicle, equipment, building) across multiple years rather than expensing it all at once.
Depreciation is fundamental to financial reporting because it connects assets to the revenue they generate. Without it, a business that invests heavily in equipment would look unprofitable in year one (full expense recorded) and artificially profitable in later years (no cost recorded). Depreciation smooths this and gives a truer picture of profitability across the asset's life.
For business owners, depreciation is an expense that reduces reported profit but doesn't involve actual cash leaving your account (the cash left when you bought the asset). This is why profit and cash flow are different. Depreciation allows you to understand the true economic cost of your business.
For tax purposes, depreciation (called capital allowances in tax contexts) is critical. It's one of the largest deductions available to businesses because assets represent real investment. Getting depreciation wrong costs money in two ways: overstating assets on the balance sheet (auditor challenge) or underclaiming tax deductions (paying too much tax).
Depreciation follows a consistent process that translates asset cost into expense over time.
The depreciation process:
Real example:
A law firm buys office furniture for $25,000. They estimate a useful life of 7 years. Using straight - line depreciation, the annual expense is $25,000 / 7 = $3,571 per year. In year 1, the income statement shows $3,571 depreciation expense (reducing profit). The balance sheet shows $25,000 furniture minus $3,571 accumulated depreciation for a net book value of $21,429. No cash left the account in year 1 beyond the initial purchase. In year 7, the book value reaches zero, and annual depreciation expense stops. If they sell the furniture in year 4 for $15,000, they record a $3,571 loss (book value was $14,146, sold for $15,000... actually a gain of $854).
Methods compared:
Straight - line is even: $10k per year across a 5 - year asset. Declining balance front - loads: Year 1 might be $4k, year 2 $3.2k, year 3 $2.56k. Declining balance is used when assets lose value faster early (cars, technology). Units of production matches depreciation to actual use (machines that run 10,000 hours in year 1 depreciate more than those running 5,000 hours). Each method spreads the same total cost but on a different schedule.
Common mistakes:
Best practices:
The most common friction point accountants see: a business has a spreadsheet for depreciation that diverges from what's actually on the balance sheet. Year 1 they set up depreciation correctly. Year 2 they acquire more assets and update the spreadsheet manually. Year 3, the spreadsheet is wrong because an asset was fully depreciated but not removed, and two assets were bought but not added. By year 5, the fixed asset schedule and the general ledger don't reconcile. This creates audit findings and makes it impossible to know whether the balance sheet is accurate. The discipline is simple: maintain one fixed asset register, update it the month each asset is acquired, review it annually for adjustments. If book value and actual useful life diverge, depreciate the remaining balance over the revised remaining life.
When you buy equipment for $10,000 and it lasts 5 years, depreciation lets you expense $2,000 per year instead of $10,000 in year one. This matches the cost to when the asset is actually generating revenue for your business. Without depreciation, your profit would be terrible in year one (because you'd expense $10,000) and great in years 2 - 5 (because there's no cost).
Any tangible asset that lasts more than one year: vehicles, equipment, machinery, office furniture, computers, buildings. NOT land - land doesn't depreciate because it doesn't wear out. And NOT items you consume quickly like office supplies, fuel, or inventory. The test: Does it have a useful life longer than one year? If yes, it can be depreciated.
Straight-line is simplest: divide cost evenly across useful life ($10,000 over 5 years equals $2,000 per year). Declining balance front-loads the expense (year 1 is highest) because assets often lose value faster early on. The method you choose affects profit each year but not total profit over the asset's life - you're just changing timing.
Tax authorities publish guidance (IRS in the US, HMRC in the UK) with standard lives for different assets. Cars are typically 5 years, buildings 27.5 - 40 years, equipment 3 - 10 years. You can't just guess; you have to justify the useful life if audited. If you depreciate a computer over 10 years when everyone knows computers last 3 - 4 years, an auditor will challenge it.
Depreciation is accounting (how you report profit). Capital allowances are tax (how you reduce taxable income). You might depreciate a van over 5 years for financial reporting, but claim capital allowances faster for tax. The two don't have to align. This is why accountants keep separate depreciation schedules for accounting versus tax.
Once an asset reaches zero book value, you stop recording depreciation expense. If you still own it and it still works, it stays on the balance sheet at zero value. When you finally dispose of it (sell or scrap), you record a gain or loss. A van you bought for $40k, depreciated to zero, then sold for $3k - you record a $3k gain. If you sell for $0, there's no gain or loss.
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