30-Day Rule Calculator (UK Crypto Tax)

Find the Earliest Date You Can Buy Back

Disposal date

Enter the date you sold, swapped, spent, or otherwise disposed of the cryptoasset.

The UK 30-day rule, often referred to as the bed and breakfasting rule, forms part of HMRC’s share matching rules for capital gains.

If you dispose of crypto and then repurchase the same token within the following 30 days, the acquisition is matched with the disposal instead of your pooled cost basis.

This calculator helps you identify the earliest date a repurchase would fall outside the 30-day window.

You’ll need:

The date you disposed of the cryptoasset

This calculator provides a date-based guide only and does not determine the final tax treatment of a transaction, which depends on your full trading history and HMRC’s share matching rules.

For a detailed explanation of how the Section 104 pool and matching rules apply to crypto, see our guide to UK share pooling and matching rules.

Get Your Full 30-Day Rule Buy-Back Schedule

Planning more than one disposal? Use the multi-asset calculator below to generate a full 30-day rule buy-back schedule across up to 20 assets.

Multi-Asset 30-Day Rule Calculator

Add each disposal you want to track. We’ll validate the schedule on the server and email you the earliest buy-back date for each asset.

You can add up to 20 disposals in total.

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We’ll use this to send your full 30-day rule buy-back schedule.

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How the 30-Day Rule Works

When you dispose of cryptoassets, you might assume the gain or loss is fixed at that point based on your existing holdings. In practice, that is not always the case.

If you buy back the same asset on the same day, or within the following 30 days, those purchases are matched with your disposal instead of your pooled cost. This can retrospectively change the gain or loss you originally expected.

Only if no matching purchases are made in that period does the disposal remain matched with your Section 104 pool (your average cost).

Example:

If you dispose of an asset on 1 March, the 30-day window runs from 2 March to 31 March (inclusive).

Any acquisitions of the same asset during this period are matched with that disposal and used as the base cost instead of your pooled cost.

The earliest date a repurchase would fall outside the 30-day window is therefore 1 April.

While the dates are straightforward, the impact is not. A buy-back within the 30-day window can change which cost is used for your disposal, meaning the gain or loss you planned for is not always the one you end up with.

Example: How a loss can turn into a gain

Clara sells 10 SOL on 1 August for £800. Her pooled cost for the disposal is £1,000.

At this point, it looks like she has made a £200 loss.

However, she buys back 10 SOL on 15 August for £600, which is within 30 days of the disposal.

The 30-day rule applies, so the disposal on 1 August is matched with the 15 August purchase instead of her pooled cost.

This changes the calculation:

Disposal proceeds: £800
Matched cost: £600

Instead of a loss, Clara now has a £200 gain.

This is why the 30-day rule matters, particularly around the end of the tax year. You may have planned your disposals to achieve a specific gain or loss for the year, only for a later buy-back within 30 days to change that outcome retrospectively. The calculator above helps you identify when a repurchase falls outside this window.

If you want to understand how these rules affect your wider tax position, including more detailed examples, see our full guide to crypto share pooling and matching.

FAQs

Does the 30-day rule apply to all crypto disposals?
It applies when you dispose of a cryptoasset and repurchase the same token within 30 days. Buying a different token does not trigger the rule.

Does the rule apply to swaps?
Yes. Swapping one cryptoasset for another counts as a disposal for UK tax purposes, so the 30-day matching rules can apply if you later repurchase the same token.

Is the 30-day window inclusive?
Yes. The rule covers the 30 days following the disposal date. The earliest date outside the window is day 31 after the disposal.