Section 104 calculator
Enter your buys and sells of one share or fund. See how HMRC matches each sale (same day, then the next 30 days, then the pool), the gain, and what is left after the annual exempt amount.
General information, not tax advice. These figures are estimates from the rules and numbers you enter; they ignore your other gains, losses and income. Check with a registered tax agent or adviser before you act.
How each sale was matched
| Sold | Matched with | Units | Proceeds | Allowable cost | Gain |
|---|---|---|---|---|---|
| 2026-10-14 | 30-day (bed and breakfast) (bought 2026-10-30) | 20 | £2,557.61 | £2,501.95 | £55.66 |
| 2026-10-14 | Section 104 pool | 80 | £10,230.44 | £6,991.96 | £3,238.48 |
By tax year
| Tax year | Gains | Losses | Annual exempt amount | Taxable gain | Est. CGT |
|---|---|---|---|---|---|
| 2026-27 | £3,294.14 | £0.00 | £3,000.00 | £294.14 | £70.59 |
Left in the Section 104 pool: 120 shares with an allowable cost of £10,487.94.
Do this for your whole portfolio. Mintage keeps every parcel, applies corporate actions and runs this before each sale.
Try with sample dataHow it works
For shares and funds of the same class, HMRC matches a sale first with shares bought on the same day, then with shares bought in the following 30 days (the “bed and breakfast” rule), and only then with your Section 104 pool at its average cost. That is why buying back within 30 days can change your gain.
Gains in a tax year above the annual exempt amount (£3,000 from 2024-25) are taxed at 18% or 24% for disposals from 30 October 2024. Shares in an ISA or pension are outside CGT, so leave them out.
See it with your own eyes in under a minute
Open a full workspace filled with sample data for the United Kingdom. No sign-up, nothing to install.
- No card needed
- Cancel anytime
- Export everything
- AU, US and UK tax aware