Blog · 8 November 2026

Set aside tax on every invoice: the percentage method US 1099 contractors use

Making Tax Digital shows you where the year is heading every quarter, but the bill still arrives once a year, on 31 January. The gap between those two facts is where sole traders get hurt: a year of income, spent as it arrived, and a tax bill with no money behind it. American 1099 contractors have the same problem in a harder form — nothing is withheld from their pay at all — and the habit that saves them is disarmingly simple: a fixed percentage of every invoice, moved into a separate account the day the money lands. Here is that method, worked out with UK 2026/27 figures.

1. The method: a percentage of profit, moved on the day you are paid

The rule is one sentence: every time a client pays you, move a fixed percentage of the profit on that invoice into a separate tax account before you spend anything. Not at month-end, not “whatever is left” — the same day, off the top. The account is not savings and it is not a buffer; it is money that was never yours. Two choices make it work: the percentage is set on profit, not turnover, and it is reviewed after every quarterly update, not once a year.

Why profit, not turnover? Because tax is charged on profit — income after allowable expenses. Setting aside 25% of turnover when your expenses run at 30% of turnover means you are locking away far more than the bill will ever be, and the pot becomes a reason to raid it. Work out your profit margin first, then apply the percentage to that.

2. What percentage? Worked UK examples for 2026/27

For 2026/27, a sole trader in England, Wales or Northern Ireland with no other income pays Income Tax of 20% on profit above the £12,570 Personal Allowance (40% above £50,270), plus Class 4 National Insurance of 6% on profits between £12,570 and £50,270 and 2% above. Inside the basic-rate band the combined marginal rate is 26% (20% + 6%); above £50,270 it is 42% (40% + 2%). Worked on profit after expenses:

Check the £40,000 row: taxable profit is £40,000 − £12,570 = £27,430. Income Tax is 20% of that, £5,486; Class 4 is 6% of the same £27,430, £1,645.80. The bill is 17.8% of profit, but the set-aside column says 20% — the extra two points are the buffer. Rates are frozen, but your income is not: a good year pushes more profit into the 40% band, and a buffer set today covers a band crossed tomorrow. At £60,000 the honest percentage is already 23.1%, so 25% is the floor, not the ceiling. If your profit is near or above £50,270, start at 30% and correct down after your first quarterly update.

3. Why the American number is higher — and what it teaches

US 1099 contractors commonly set aside 25–30% of every payment, and the arithmetic explains why: their self-employment tax alone is 15.3% on 92.35% of profit — effectively 14.13% — before a dollar of income tax. A contractor on $80,000 of profit owes $11,303.64 of self-employment tax plus income tax on top, for a total federal bill of $16,647.47. The UK equivalent is lighter at the same income because Class 4 is 6%, not 12.4%, and the Personal Allowance shelters the first £12,570 entirely. The lesson is not the percentage; it is the discipline. American contractors learn it because the IRS makes them pay quarterly — four bills a year, or a penalty figured quarter by quarter. MTD asks you to report quarterly and pay once, which is gentler on paper and more dangerous in practice, because nothing forces the money aside until January. If you want the US comparison in full — the two systems side by side on the same income — the 1099 vs W-2 calculator runs it for tax year 2026, and how much more a 1099 contractor should earn than a W-2 employee shows what a contractor has to charge to end up equal after tax and benefits.

4. Reset the percentage after every quarterly update

A fixed percentage is a starting guess, not a plan. Your quarterly updates show your cumulative position for the year, so each one is a chance to re-estimate: take the year-to-date profit, annualise it, and check the table above. If the second update shows you heading for £55,000 instead of £40,000, the right percentage is already 25%, not 20% — and you have two quarters left to catch up, not ten days in January. Check your own dates on the MTD quarterly deadline calendar (7 August, 7 November, 7 February, 7 May) and put the re-estimate in the diary alongside the submission itself. The update tells you the period; the percentage tells you the money.

5. The three mistakes that empty the pot

First, setting aside on turnover instead of profit, which locks away too much and teaches you to raid the account. Second, forgetting Class 4 — it is only 6%, so it is easy to leave out, and at £40,000 of profit it is £1,645.80 of the bill. Third, treating the pot as available when a slow month arrives. A separate account with no card attached is not an inconvenience; it is the whole mechanism. If the money is one tap away, it is not set aside.

Sources

• GOV.UK — Income Tax rates and Personal Allowances (£12,570 Personal Allowance; 20% basic rate to £50,270; 40% higher rate; 2026/27)
• GOV.UK — Self-employed National Insurance rates (Class 4: 6% on profits £12,570–£50,270, 2% above; 2026/27)
• GOV.UK — Quarterly updates: periods and deadlines (standard periods and 7 August / 7 November / 7 February / 7 May deadlines)
• IRS — Self-employment tax (Social Security and Medicare taxes) (15.3% on 92.35% of net earnings; US comparison figures)

Free information tool — not tax advice. UK figures are for 2026/27 (6 April 2026 to 5 April 2027), England, Wales and Northern Ireland, for a sole trader with no other income; Scotland sets its own Income Tax rates, and your position may differ. US figures are tax year 2026 and illustrative only. Confirm your own position with HMRC or an accountant.