Hybrid Writing Down Allowance Calculator

UK HMRC Publications & Guidance

Published April 1st, 2026

Detected April 1st, 2026

Summary

HMRC published guidance and a calculator on 1 April 2026 to help entities determine their hybrid writing down allowance rate when accounting periods span the rate change from 18% to 14%. The hybrid rate applies separately to Corporation Tax (effective 1 April 2026) and Income Tax (effective 6 April 2026).

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What changed

HMRC issued guidance on 1 April 2026 explaining how to calculate a hybrid rate of writing down allowance for accounting periods that include the date when the main rate changed from 18% to 14%. The guidance provides both a manual calculation method (8-step process) and an online calculator tool. The rate change applies differently to Corporation Tax (1 April 2026) and Income Tax (6 April 2026).

Any entity with an accounting period that spans the rate change date must use the hybrid rate calculation to determine their writing down allowance. Entities should identify their accounting period dates, count the days before and after the rate change, apply the respective rates (18% and 14%), and combine the results. The guidance includes a worked example showing a company with a 1 January to 31 December 2026 accounting period resulting in a hybrid rate of 14.99%. This is an informational tool to ensure correct claims; no new compliance obligations are created beyond existing capital allowances rules.

Source document (simplified)

Guidance

Calculate your hybrid rate of writing down allowance

Use this calculator to work out your hybrid rate of writing down allowance, if your accounting period includes the day the rate changed.

From: HM Revenue & Customs Published 1 April 2026 Get emails about this page Print this page The main rate of writing down allowance changed from 18% to 14% on:

1 April 2026 for Corporation Tax
6 April 2026 for Income Tax If your accounting period includes the date when the rate changed, you’ll need to work out a hybrid rate to use for that accounting period.

Your hybrid rate is worked out based on what how much of your accounting period is before the rate changed, and how much is after.

Before you start

You’ll need to know:

which tax you pay
the start date of your accounting period
the end date of your accounting period Start now

How to work out your rate manually

If you want to work out your hybrid rate, you should:

Count the number of days in the whole accounting period.
Count the number of days from the first day of the accounting period to the day before the rate changed, including the first day.
Divide the days before the rate changed by the total number of days.
Multiply the result by 18.
Count the number of days from the day the rate changed to the end of the accounting period, including the day the rate changed.
Divide the days from when the rate changed by the total number of days.
Multiply the result by 14.
Add the result from step 4 to the result from step 7. If the number has more than 2 decimal places, round up to 2 decimal places. This number is your hybrid rate.

Example

A company that pays Corporation Tax has an accounting period beginning on 1 January 2026 and ending on 31 December 2026.

In the accounting period there are:

365 total days
90 days before 1 April 2026
275 days after 1 April 2026 (including 1 April 2026)
To work out their hybrid rate, the company should:
divide 90 by 365, and multiply the result by 18
divide 275 by 365, and multiply the result by 14
add the two results together
round up to 2 decimal places
Their hybrid rate for this accounting period is 14.99%.

What to do with your hybrid rate

Use your hybrid rate to work out what writing down allowances you can claim.

You need to do more calculations to adjust the amount of writing down allowances you can claim if your accounting period is more or less than 12 months.