Annual Investment Allowance Timing: A 2026/27 Tax Guide

Quick answer

Time your Annual Investment Allowance purchases so the 100% deduction lands in the accounting period where it saves the most tax. Bring spending forward into a high-profit year, or one where it pulls profit through the 40% band, the Class 4 NI 6% band, or Corporation Tax marginal relief. Delay it when next year's profit -- and tax rate -- will be higher.

What the Annual Investment Allowance does

The AIA is a capital allowance. When you buy qualifying plant and machinery -- tools, equipment, computers, commercial vehicles, fixtures and fittings -- you would normally relieve the cost slowly through writing-down allowances over many years. The AIA instead lets you deduct the whole qualifying cost from your taxable profit in the period the expenditure is incurred, up to an annual cap.

That immediate 100% deduction is what makes timing so important. The relief is tied to your accounting period, so the date the spend is incurred decides which year's tax bill it reduces. Move that date, and you move the tax saving.

Cars are the headline exclusion. They never qualify for AIA and are handled through emissions-based writing-down allowances instead. Vans, lorries and most commercial vehicles are not "cars" for this purpose and can qualify. Buildings, land and items you lease out have their own rules, so check qualifying status before assuming a purchase counts.

Why timing changes the tax you save

The saving from a deduction equals the deduction multiplied by your marginal tax rate. A GBP 10,000 AIA claim is worth far more when it strips income out of a 40% band than out of a 20% band. So the question is never just "can I claim?" -- it is "in which period does this claim save the most?"

When expenditure is incurred

For AIA the key date is when expenditure is "incurred", which is generally when there is an unconditional obligation to pay -- usually contract or delivery date, not when cash leaves your account. There are special rules where payment falls due more than four months later. Near a year-end, a few days either side of the incurred date can shift the whole deduction into a different tax year, so confirm the date with your accountant.

Sole traders: Income Tax and Class 4 NI together

For a sole trader, AIA reduces taxable trading profit, which feeds into both Income Tax and Class 4 National Insurance. In 2026/27 the figures that matter are:

*The 60% effective band reflects the personal allowance tapering away by GBP 1 for every GBP 2 of income above GBP 100,000, reaching zero at GBP 125,140.

The lesson is stark. An AIA deduction that pulls profit down out of the 40% band saves 42% (Income Tax plus 2% NI). A deduction that only reduces profit already inside the basic-rate band saves 26%. And a deduction that drops profit through the GBP 100,000 to GBP 125,140 zone can save an eye-watering 62% on that slice. If you expect to cross GBP 100,000 this year but not next, timing a qualifying purchase to land now is unusually valuable.

Model the before-and-after picture with a

so you can see the combined Income Tax and NI effect of the deduction in each period before you commit.

Companies: mind the marginal relief band

Limited companies face a different calculation. Corporation Tax in 2026/27 is 19% on profits up to GBP 50,000 and 25% above GBP 250,000, with marginal relief tapering the rate between those points. Because of how that taper works, the effective marginal rate inside the GBP 50,000 to GBP 250,000 band is higher than 25% on the affected slice -- which makes AIA claims that pull profit down through this band especially efficient.

So a company sitting in the marginal band can save tax at an effective rate above 19% by timing the claim into the higher-profit period. A company already comfortably under GBP 50,000 saves only 19%, so deferring the claim to a fatter year may be smarter.

Full expensing versus AIA for companies

Companies also have full expensing -- a 100% first-year deduction for qualifying new and unused main-pool plant and machinery, with no annual cap. AIA still earns its place for assets full expensing does not cover, such as certain second-hand items. Unincorporated businesses cannot use full expensing at all, so AIA remains their primary route to an upfront 100% deduction. Decide asset by asset which relief applies.

Run your numbers through a

to see how a claim moves you across the marginal relief band in each candidate year.

Three practical timing moves

1. Pull spend into a high-profit period. If this year's profit is higher than next year's expected profit -- or sits in a costlier band -- bring qualifying purchases forward so the deduction relieves the most expensive income.

2. Split purchases around the year-end. If a single large outlay exceeds your available AIA limit, consider whether incurring part of it before the year-end and part after lets you claim full AIA on more of the cost across two periods, rather than dumping the excess into the slow-relief pool.

3. Claim less, deliberately. Because AIA is a claim, you can restrict it. If a full claim would waste your GBP 12,570 personal allowance or drag profit below where it relieves tax efficiently, claim a smaller amount and carry the rest forward as writing-down allowances.

What happens above the limit

Spending more than your available AIA does not lose relief. The excess enters the normal capital allowances pool and attracts writing-down allowances over future years -- you simply get the relief more slowly. That is why, for businesses planning heavy investment, spreading qualifying spend across accounting periods to keep more of it inside the AIA cap can accelerate cash savings.

A worked illustration

Suppose a sole trader expects GBP 60,000 of profit this year and GBP 45,000 next year, and plans to buy GBP 9,000 of qualifying equipment. Claim it this year and the deduction strips GBP 9,000 from profit taxed at 40% Income Tax plus 2% NI -- a 42% saving, roughly GBP 3,780. Defer it to next year and the same GBP 9,000 reduces profit taxed at 20% plus 6% NI -- a 26% saving, around GBP 2,340. Same asset, same cost, but timing the claim into the higher-profit year is worth roughly GBP 1,440 more.

This is an illustration of the mechanism, not advice on your situation. Confirm the incurred date, the asset's qualifying status, and your projected profit with your accountant before acting.

Common mistakes to avoid

• Assuming the payment date is the relevant date. It is usually the incurred date -- contract or delivery -- that decides the period.
• Treating a car as qualifying. Cars never get AIA; use writing-down allowances or AMAP mileage instead.
• Claiming the full AIA reflexively in a low-profit year and wasting allowances or band headroom.
• Forgetting the limit is time-apportioned in a short accounting period.
• Overlooking full expensing, which may be the better route for a company buying new main-pool assets.

Bottom line

The Annual Investment Allowance gives generous upfront relief, but its value depends almost entirely on when you claim it. Match the deduction to the period where your marginal rate is highest -- whether that is the 42% or 62% zone for a sole trader, or the marginal relief band for a company -- and you turn a routine purchase into a deliberate tax decision. Model both years first, confirm the incurred date, and only then sign the order.