Behind on Self Assessment? A Step-by-Step Catch-Up Plan

If you are behind on Self Assessment, the fastest way out is to establish exactly which years are outstanding and then file the oldest one first — even if you cannot pay what you owe yet. Filing and paying are separate obligations, and filing is the one that stops the problem growing.

Being behind is more common than people assume, and it is almost always fixable. What makes it worse is waiting, because penalties and interest accumulate while nothing is happening. Here is a practical order of work, with the autumn deadline dates that matter if you want to get current this year.

Key takeaways

• File first, then deal with payment. They are separate obligations with separate penalties.
• Work out precisely which years are missing before you submit anything.
• Late filing penalties escalate over time and can apply even when no tax is due.
• Contacting HMRC yourself is generally viewed more favourably than waiting for HMRC to contact you.
• Time to Pay arrangements exist for people who cannot pay in one go.

What "behind" actually means

A Self Assessment return is late once the filing deadline for that tax year has passed. For a tax year ending 5 April, the online filing deadline is 31 January following the end of that tax year, and the paper deadline is the preceding 31 October.

So for the 2025/26 tax year, which ended on 5 April 2026: a paper return is due by 31 October 2026, an online return by 31 January 2027, and the balancing payment is also due by 31 January 2027. If you have only recently become self-employed, note that you also needed to register by 5 October 2026 — our guide to the Self Assessment registration deadline covers what to do if you missed it.

Step one: find out which years are outstanding

Do not guess, and do not start from the oldest thing you can remember. Sign in to your HMRC online account and look at your Self Assessment record, which shows returns received and returns outstanding. If you cannot access the account, HMRC's correspondence will normally list the years in question, and you can contact HMRC to confirm.

Write the list down. Two or three specific years is a manageable task. "A few years of mess" is not, and the vagueness is usually what keeps people stuck.

Step two: understand what the delay is costing

Self Assessment late filing penalties escalate in stages: an initial fixed penalty once the deadline passes, then daily penalties if the return is still outstanding after a further period, then additional penalties at six and twelve months which are calculated by reference to the tax due. Late payment attracts separate penalties and interest.

Penalty rules have been reformed in stages as Making Tax Digital rolls out, so do not rely on a figure you read in an old article. Check the current amounts and triggers on GOV.UK's Self Assessment penalties page.

One point worth knowing: the initial fixed penalty can apply even if you owe no tax at all for that year. "I would not have owed anything anyway" is not a reason to leave a return unfiled.

Filing versus paying, side by side

Step three: rebuild the records

For each outstanding year you need income and allowable expenses. Most of it can be reconstructed even if nothing was kept at the time.

1. Download bank statements for each tax year, 6 April to 5 April.
2. Pull platform or client summaries for the same periods, such as annual statements from a marketplace or app.
3. Request duplicate invoices from regular suppliers where receipts are missing.
4. Check your HMRC record for any employment income and tax already deducted.
5. Separate business from personal spending line by line, and be realistic about mixed use.
6. Keep a short note explaining any figure you had to estimate, and how you arrived at it.
7. File the oldest outstanding year first, then work forward.

Claim what you are genuinely entitled to and no more. Inflating expenses to reduce a bill turns a late filing problem into a far more serious one, and HMRC treats deliberate errors very differently from honest lateness.

Step four: deal with the payment

Once the returns are filed you will know the total. If you cannot pay it immediately, HMRC offers Time to Pay arrangements that spread the debt over instalments. Some people can set one up online within certain limits; others need to phone. Interest continues to run on the outstanding amount. The current criteria are on GOV.UK's guidance on difficulties paying HMRC.

Contact HMRC before the debt is passed to collections rather than after. An arrangement agreed early is a straightforward administrative process.

Worked example (illustrative example)

"Selma", an invented illustrative example, started working for herself in 2023 and filed her first return. Life got busy and she filed nothing for the two tax years after that. By autumn 2026 she was avoiding the post.

Her first step was not filing. It was logging in and confirming that exactly two years were outstanding, not four as she had feared. That single check took fifteen minutes and changed how the task felt.

She then downloaded three years of bank statements, pulled her annual platform summaries, and reconstructed income and expenses year by year. She filed the older year first, then the more recent one, which meant late filing penalties stopped accruing. Only then did she look at the total owed and contact HMRC about instalments. The order mattered more than the speed. This is an invented example used to show the sequence, not a prediction of anyone's outcome.

Common mistakes

• Waiting until you can pay before you file. This is the single most expensive mistake, because filing penalties keep building.
• Guessing which years are missing. Check the record first.
• Starting with the most recent year. Older years usually carry the larger accumulated penalties.
• Assuming no tax due means no penalty. The fixed late filing penalty can still apply.
• Inflating expenses to reduce the bill. It converts a correctable problem into a much more serious one.
• Ignoring HMRC letters. Engaging voluntarily is generally treated more favourably than being chased.

Getting help with it

Catch-up work is a normal part of what accountants do, and it is not something to feel awkward about. Our personal tax service starts from £180 per year and covers preparing and filing Self Assessment returns, including earlier years. Once you are current, our bookkeeping service from £150 per month keeps records in order so it does not happen again — and our guide to bookkeeping vs doing it yourself sets out both options honestly.

If you would rather talk it through than read about it, contact us or see our pricing. We work on fixed fees, so you will know the cost before anything starts.