The UK tax year ends on 5 April, and a set of investment allowances goes with it. Nothing rolls over. Nothing is topped up retrospectively. Nobody at HMRC will ring to remind you. An hour with your statements in March is usually enough to make sure you are not handing over tax you did not need to pay.

What follows is a working checklist for investors, not a tax return guide. Work through it in order and you will cover the allowances that matter most.

Start with the ISA allowance

Every adult has a £20,000 ISA allowance for the tax year, and it is the most straightforward shelter available: dividends, interest and capital gains inside the wrapper are free of UK tax. Use it or lose it.

Some practical points people miss:

• The allowance is shared across cash ISAs, stocks and shares ISAs, innovative finance ISAs and Lifetime ISAs. A Lifetime ISA contribution of £4,000 counts towards your £20,000.
• Each partner has their own allowance, so a couple can shelter £40,000 between them. You cannot invest your money under someone else's name, but you can gift money to a spouse or civil partner and they can invest it.
• Transferring an existing ISA to a new provider does not use up allowance. Paying new money in does.
• If you are unsure what to buy, many platforms let you hold the cash inside the ISA temporarily. That is often better than leaving it outside and losing the allowance.

If you hold the same investments in a general dealing account, "bed and ISA" — selling outside the wrapper and buying inside it — is a common move. Be aware of the 30-day rule, explained below, because buying the same holding back within 30 days can change the capital gains calculation in ways people do not expect.

Top up the pension — and check the limits first

Personal pension contributions have to reach the provider, and be allocated, by 5 April to count against this tax year. That is a real deadline, not a soft one, and it is earlier in practice if you are paying in by bank transfer or cheque.

Contributions attract tax relief at your marginal rate, subject to rules. Broadly, you can get relief on the higher of your relevant UK earnings and £3,600. The annual allowance is £60,000, and you may be able to carry forward unused allowance from the previous three tax years, which is useful if your contributions have been uneven.

Two complications worth checking before you write a large cheque:

High earners

The annual allowance tapers for those with higher incomes, down to a minimum of £10,000, so a generous top-up can create a charge rather than a benefit. Run the numbers first.

Flexible access

If you have already flexibly accessed a defined contribution pension, the money purchase annual allowance applies and is much lower — commonly £10,000.

If you are employed, remember that salary sacrifice contributions follow the payroll date, not the date you decide to do it. Higher and additional rate relief on personal contributions usually needs to be claimed through self-assessment.

Review capital gains before you sell anything

The capital gains tax annual exempt amount is £3,000 per person. Gains below that are not taxed, and the allowance cannot be carried forward. For most investors this creates a simple annual decision: is there a holding with an unrealised gain that would be sensible to realise anyway?

Options worth considering:

• Do nothing. If you expect to hold for decades, or your gains are small, there is no obligation to act.
• Realise a gain up to the exemption. You can sell and hold the cash, or reinvest in something different.
• Bed and ISA. Sell outside the wrapper and repurchase inside it, so future growth is sheltered.
• Transfer to a spouse or civil partner. Transfers between spouses are treated as no gain, no loss, so the gain can be realised by the person with more unused exemption or a lower rate band.

Above the exemption, gains on shares are taxed at 18% where they fall within your basic rate band and 24% above it for disposals made since 30 October 2024, with the rate band affected by your other income. Rates and thresholds do change, so check the current position before you deal.

One rule catches people out every March: the 30-day "bed and breakfast" rule. If you sell shares or funds and buy the same holding back within 30 days, the repurchase is matched against the sale rather than treated as new, and your base cost changes. Buying back inside an ISA counts for this purpose. Check before you sell and repurchase in a hurry.

Use your losses, and keep the evidence

Capital losses are more valuable than most people realise, and they can be claimed even in years when you have no gains to offset. There is a four-year window to report a loss to HMRC, so dig out old contract notes if you sold something at a loss and never told anyone.

Reporting is a separate question from paying. You generally need to report disposals through self-assessment where the total proceeds in the year exceed £50,000, even if no tax is due. Residential property disposals need a separate return and payment within 60 days of completion. This area is easy to get wrong, so if your affairs are messy or the numbers are large, an accountant earns their fee.

The smaller allowances people forget

• Dividend allowance: £500 of dividends a year are tax-free, with amounts above taxed at rates that depend on your band.
• Personal savings allowance: £1,000 for basic rate taxpayers, £500 for higher rate, and nothing for additional rate.
• Trading allowance: £1,000 of property or trading income, useful if you have a small side activity alongside your investments.
• Gift Aid: charitable donations extend your basic rate band, which can reduce the tax on gains and dividends. If you make regular donations, check they are recorded.
• Marriage allowance: a transfer of part of the personal allowance between spouses where one has low income.

A sensible order of operations

1. Add up what you have already used this tax year across ISAs and pensions.
2. Fill the ISA allowance — cash or investments, whichever suits you.
3. Check pension headroom, including carry forward, before contributing.
4. Look at unrealised gains and decide whether to use the £3,000 exemption.
5. Report any old losses you have not claimed.
6. File the paperwork somewhere you will find it next year.

Do not leave it to the last afternoon

Platforms get busy in the final week of the tax year. Deals take time to settle, bank transfers take a day or two, and pension providers have their own cut-off times that are earlier than 5 April. Aim to have everything done by the middle of March, with a week in hand for anything that goes wrong.

Finally, a reminder: this is general information about how the allowances work, not personal advice. If you are near a threshold, have a complicated mix of income, or are unsure how the rules apply to you, speak to a regulated adviser or a tax accountant before acting.

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