There is a particular kind of sinking feeling that comes with opening a tax bill in January and realising the money simply is not there. It happens to capable, hardworking business owners every year, and it almost never happens because they spent the money on something frivolous. It happens because a client payment landed in the current account, looked like profit, and quietly became groceries, software subscriptions and a new laptop.

The fix is not complicated. It is a habit: every time money comes in, a set percentage goes straight into a separate savings pot. Do that consistently and the deadline stops being frightening.

Why the bill always feels bigger than you expect

A £10,000 invoice does not mean £10,000 for you. If you are a sole trader in the basic rate band, income tax at 20% and Class 4 National Insurance at 6% take roughly £2,600 of it. If you are registered for VAT, another chunk of what you collected was never yours to begin with.

Then there is the twist that catches most people in their first profitable year: payments on account. HMRC assumes next year will look roughly like this year, so it asks for half of your expected bill on 31 January and the other half on 31 July. You pay your first bill in January, breathe out, and then find a second demand sitting alongside it. Plenty of freelancers have had a genuinely good year and still ended up on a payment plan.

Work out your percentage and be honest about it

You do not need perfect accuracy. You need a number that is slightly too high rather than slightly too low. As a rough starting point:

• Sole trader in the basic rate band: set aside 25–30% of every payment.
• Sole trader in the higher rate band: 40–45%, because you are paying 40% income tax plus Class 4 NIC.
• Limited company director taking a salary and dividends: 30–40% for corporation tax and dividend tax combined, depending on your profit level.
• Anything registered for VAT: add the VAT element on top, ideally in its own pot so it never mingles.
• Student loan repayments: add another 9% if you are on Plan 2, or 6% on Plan 1.

If you are in your first year of self-employment, use 30% and expect the payments on account to make the second January feel heavier. That is normal, and it settles down once the system catches up with you.

Open a separate pot and treat it as untouchable

Money held in the same account you buy lunch from is not really set aside. Open a dedicated instant access savings account, name it something blunt like "Tax", and do not link a card to it. Instant access matters — you need the money to be available on 31 January, not tied up in a twelve-month fix you cannot break without losing interest.

The point is friction. When transferring money back takes two minutes and a login, you will think twice. That small delay is often the whole difference between paying your bill and arranging a Time to Pay plan.

Make the transfer part of every invoice

Tie the transfer to the moment money arrives, not to a monthly intention. The sequence is simple: payment clears, you move the percentage, then you look at what is left. If you wait until the end of the month, the remainder has usually already been allocated in your head.

For regular retainers, set up a standing order the day after your usual payment date. For lumpy project work, do it manually within 24 hours — the longer you leave it, the easier it is to talk yourself out of it. Some people go further and open a second current account just for tax, which makes the transfer feel like a bill being paid rather than savings being raided.

Know the dates that actually matter

Setting money aside is easier when you know exactly what you are saving for:

• Self Assessment: 31 January for the balancing payment plus your first payment on account, and 31 July for the second payment on account.
• Corporation tax: nine months and one day after the end of your accounting period.
• VAT: usually one month and seven days after the end of each quarterly period if you file online and pay by direct debit.
• PAYE: the 22nd of the following month, or the 19th if you pay by post.

Review your percentage at least twice a year, in roughly April and October. If your profit is running ahead of forecast, nudge the rate up. If it has dipped, you can reduce it — but only after checking the numbers properly rather than hoping.

If you are already behind, start from today

Being short is not a moral failing, and it is far more common than the confident LinkedIn posts suggest. If a bill is looming and the pot is empty, contact HMRC before the deadline rather than after it. A Time to Pay arrangement lets you spread the cost in instalments, and interest on late payment is an avoidable expense you do not want to add to an already difficult month.

Then reset. Pick your percentage, open the pot, and apply it to the very next payment that lands. One good quarter of consistent transfers is usually enough to turn the January dread into a mildly boring admin task — which is exactly what a tax bill should be.