Depreciation and other amounts written off assets

That's correct behaviour — depreciation isn't tax-deductible in the UK, so it gets added back in the tax computation. You claim tax relief on assets through capital allowances instead.

The way it works:

- Enter your depreciation figure in the P&L section — TinyTax automatically adds it back as a disallowable expense
- In the Tax Computation section, enter your Annual Investment Allowance (AIA) — this is the tax deduction for the actual cost of qualifying assets you bought this year

The AIA is usually the full purchase cost of qualifying assets (equipment, computers, machinery, etc.), not the depreciation amount. If your AIA claim equals your depreciation, they broadly cancel each other out and the net effect on taxable profit is close to zero.

More detail here: tinytax.co.uk/support/capital-allowances-aia