Self Assessment 2024/25: Deadlines, Penalties and What to File

Quick answer

If you're filing online for the 2024/25 tax year, you have until 23:59 on 31 January 2026 to:

1. File your Self Assessment tax return, and
2. Pay any tax you owe.

Both deadlines fall on the same day. Miss either and HMRC charges penalties — file-late penalties are flat fees, pay-late charges accrue 7.5% interest plus surcharges at fixed intervals.

Who needs to file Self Assessment for 2024/25?

You must file if any of these apply:

• You were self-employed with turnover over £1,000.
• You were a partner in a business partnership.
• You had untaxed income over £1,000 (side hustle, rental, freelance, crypto, OnlyFans, eBay/Vinted reselling at scale).
• You had rental income (from £1,000+, before expenses).
• You had savings interest above your Personal Savings Allowance (£1,000 basic-rate, £500 higher-rate, £0 additional-rate).
• You had dividend income above £500 (the dividend allowance for 2024/25 — note it dropped from £1,000).
• You had capital gains above the £3,000 annual exempt amount.
• Your total income exceeded £150,000 (the additional-rate threshold from 2023/24).
• You or your partner earned over £60,000 and one of you received Child Benefit (High Income Child Benefit Charge — HICBC, with the threshold raised from £50k from 6 April 2024).
• You had foreign income to declare.
• You're a company director with extra income to report.
• You claim Marriage Allowance as a transferring partner with mixed sources.

You don't need to file if your only income is PAYE wages and tiny amounts of savings interest within your PSA.

The full date map for 2024/25

The penalty structure (and how it stacks)

Late filing penalties are fixed and independent of whether you owe tax:

So even with zero tax owed, filing 12 months late costs you £1,600 minimum (£100 + £900 + £300 + £300).

Late payment penalties on top:

• 30 days late: 5% of unpaid tax.
• 6 months late: another 5%.
• 12 months late: another 5%.
• Plus 7.5% interest compounding daily.

Common things first-timers miss

1. Registering on time. If 2024/25 was your first Self Assessment year, you had to register by 5 October 2025. Missing this triggers a separate penalty.
2. Payments on account. When you owe over £1,000 in tax, HMRC asks you to pay 50% of next year's expected tax up-front on 31 January and 31 July. First-time filers often miss this and get hit with a much bigger January bill than expected.
3. Side income from platforms. From January 2025, eBay, Vinted, Etsy, Airbnb and similar platforms report seller earnings directly to HMRC. The £1,000 trading allowance still applies, but cross-checking is now automated.
4. Crypto gains. Each disposal (sell, swap, gift) is a CGT event. Many filers forget that swapping ETH for SOL is a disposal even if no GBP touched their bank.
5. Foreign dividends. US dividends are subject to 15% US withholding tax (with W-8BEN). UK higher-rate dividend tax of 33.75% still applies, with double-tax relief.
6. Wrong reference number. Paying with the wrong UTR or reference means HMRC can't match the payment and you get a late-payment penalty despite paying on time.
7. Submitting from the wrong account. HMRC personal Government Gateway and HMRC business accounts are separate. Self-employed sole traders file from the personal one.

What to gather before you start

• UTR (10 digits, on every HMRC letter to you).
• National Insurance number.
• P60 / P45 / P11D from any employment.
• Bank interest certificates (from each bank, if interest is above PSA).
• Dividend statements for non-ISA holdings.
• Capital gains records — disposals, costs, dates.
• Self-employed bookkeeping — turnover, expenses by category.
• Pension contribution statements (especially for relief-at-source claims).
• Gift Aid donation records.
• Foreign income in £ at HMRC published rates.
• Marriage Allowance decision — receiving or transferring.

What if you owe but can't pay?

HMRC offers Time to Pay arrangements:

• Owe under £30,000? You can set up online without speaking to anyone — usually 6–12 monthly instalments.
• Owe over £30,000? You have to call. They'll still arrange a plan, with longer terms possible.
• Interest at the prevailing rate (7.5%) still accrues during the plan.
• Late-payment penalties at 30 days, 6 months, 12 months don't apply if a Time to Pay plan is in place.

The plan must be agreed before the 31 January deadline to avoid the 5% surcharge at the 30-day mark.

After you file — refund or balance

If HMRC owes you money (e.g. you overpaid through payments on account, or claimed Marriage Allowance), refunds usually arrive within 5–10 working days via BACS once you've provided bank details. Some refunds come as a cheque if you don't supply bank details.

If you owe HMRC, payment options:

• Bank transfer / Faster Payment (fastest, often same-day clearing).
• Direct Debit (must be set up ≥5 working days before deadline).
• Debit card via gov.uk (no fee).
• Credit card has been disallowed since 2018.
• Cheque (must arrive 3 working days before deadline — risky).

See it in numbers

If you're self-employed or have a side hustle and want to model the impact of an extra £5k–£20k of side income:

Or for the income-tax-specific view:

Sources

• HMRC: Self Assessment tax returns
• HMRC: Self Assessment: penalties for late filing
• HMRC: HMRC interest rates for late and early payment
• HMRC: If you cannot pay your tax bill