The usual answer is a flat percentage of everything you earn. It is easy to remember and, for most therapists, wrong — here is the number that comes out of the actual arithmetic.
The advice everyone gives is to put aside 25% or 30% of what comes in. It is memorable, and for most therapists it is wrong — on a small practice by a factor of 8. Two things make it wrong. You are taxed on your profit, not on your fees, so the costs of running your practice come out before HMRC takes a view. And the percentage is not fixed: it climbs with what you earn, from about 4% on a small practice to 29% on a busy one.
Below is what to actually set aside, worked with the same engine as the Practik calculator — per session, which is the only unit that is any use when the money is arriving one client at a time.
| Your practice | Profit | Tax & NI | % of profit | Per session | Per month |
|---|---|---|---|---|---|
| 8 a week at £50 | £14,800 | £580 | 4% | £1.58 | £48 |
| 12 a week at £55 | £26,760 | £3,689 | 14% | £6.68 | £307 |
| 15 a week at £60 | £37,800 | £6,560 | 17% | £9.51 | £547 |
| 20 a week at £70 | £60,800 | £14,225 | 23% | £15.46 | £1,185 |
| 25 a week at £80 | £88,400 | £25,817 | 29% | £22.45 | £2,151 |
Read the per session column. That is the figure worth knowing, because it turns a once-a-year problem into a decision you make every time someone pays you: this much is yours, this much was never yours.
At 8 clients a week at £50, the bill is £580 on £14,800 of profit — 4%. Setting aside 25% of your fees there would have you sitting on around £4,600 against a bill of £580. Most of the first £12,570 you earn is covered by the personal allowance, and a practice that is still building rarely gets far past it.
At 25 clients a week at £80 it is £25,817 on £88,400 of profit — 29% — because a large slice now falls in the 40% band. There the rule of thumb is roughly right, which is presumably where it came from.
Over-reserving is not dangerous, just expensive: it is your money, sitting idle, in the years you most need it for training, rooms and marketing. Under-reserving is the dangerous direction, which is why the flat rule persists. The way out of choosing between them is to use the real number.
Your taxable profit is your fee income minus the genuine costs of running the practice — supervision, professional membership, insurance, room hire, CPD, your practice phone, the share of your home you work from. Those come out first. On what is left you pay:
Class 2 National Insurance is not in these figures: it stopped being payable for most sole traders, though it can still be paid voluntarily to protect a State Pension record if profits are very low. Everything here assumes sole trader status and 2025/26 rates for England, Wales and Northern Ireland — Scotland has its own income tax bands.
This is the part the percentage rules never mention, and it is the reason careful people still get caught. If your tax bill comes to more than £1,000, HMRC does not simply collect it — it also asks for a payment on account towards next year: half your bill again, due the same day, and another half the following 31 July.
So in your first proper year of practice, the 31 January payment is not your bill. It is one and a half times your bill. At 15 clients a week at £60, that is £6,560 owed and £9,840 to find on the day. It evens out afterwards — later years are a balancing payment plus the next instalment — but the first one is a step, and a set-aside pot built for £6,560 is £3,280 short.
Practices below the £1,000 threshold — 8 clients a week at £50 in the table above comes to £580 — are not asked for payments on account at all, which is another reason the flat percentage misleads at the small end.
Move the money when the client pays, not at the end of the month. A separate account, a standing transfer of the per-session figure, and the decision is made once rather than every January. If you take card payments the same logic applies to the payout rather than the session.
Recalculate when something changes. The percentage is not a constant: raise your fee by £10 or add three clients a week and it moves, because more of your profit sits in a higher band. That is the whole reason a fixed percentage cannot be right for long.
One more thing on the horizon. Making Tax Digital for Income Tax is phased in on gross income, not profit — so it arrives sooner than most therapists expect. At 20 clients a week at £70, gross fees of £64,400 bring you into it from April 2026: quarterly digital updates instead of one annual return.
Your fee, caseload and costs are not the ones in the table. Put your own in and the set-aside figure comes out with them — three questions, no sign-up.
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