Register, file, pay

  1. Register for Self Assessment if your gross trading income is over £1,000 in a tax year. Deadline to tell HMRC is 5 October after that year ends (5 October 2026 for 2025/26).
  2. Keep income and expense records as you go. HMRC can ask for them for at least five years after the 31 January filing deadline.
  3. File the online return by 31 January 2027 for 2025/26 (paper was 31 October 2026). Pay the balancing payment the same day.
  4. If last year’s bill was over £1,000, Payment on Account is due 31 January and 31 July, each 50% of that bill.

Full deadline calendar and penalty ladder.

What goes on the self-employment pages (SA103)

Turnover is all session fees, packages, online products and any affiliate income that is part of the coaching trade. Desk fees are rent. CPD is training. Platform fees are other/financial. If you also sell merch, include it or keep a clearly separate hobby (HMRC will not care what you called it if it is clearly the same business).

Deadlines and penalties

Miss the online deadline and the late-filing penalty is £100 immediately, even if you owe no tax. After three months it is £10 a day (capped at £900). At six and twelve months HMRC add 5% of the tax due or £300, whichever is greater. Late payment is a separate 5% at 30 days, six months and twelve months, plus interest.

Mistakes personal trainers make on the return

  • Leaving PayPal or Stripe balance transfers out because “that was the online stuff”.
  • Claiming a whole clothing haul.
  • Treating a second gym you visit twice a week as always-business mileage from home.
  • Not registering because the gym “takes tax off”. Check the payslip. Desk-fee contractors do not have tax taken off.
  • Putting package deposits in a drawer and declaring them next year when you deliver the sessions, while using cash basis.

If you are employed as a gym instructor and self-employed as a PT in the same building, keep the two piles of money separate. The PAYE job does not cover the PT income.

← Personal trainer tax overview · Expenses · Do I need to register?

Common questions

A client paid for 12 weeks in April. When is it income?

On cash basis, when you received it. Most small PTs use cash basis.

The gym pays me through the till. Is that PAYE?

Only if they deduct tax and NI and give you a payslip. A contractor payout is usually your turnover.