Side Hustle Tax Set-Aside Estimator 2025-26 & 2026-27 (England, Wales & NI): How Much to Put Aside for Income Tax + Class 4 NI (Excel & Google Sheets)

Type your wages, side-hustle income and costs, and see a rough estimate of the extra Income Tax and Class 4 National Insurance, the % of each payment to put aside, and a monthly pot. Every rate linked to GOV.UK. Works in Excel and Google Sheets.

"How much should I put aside for tax?" is the question every side hustler asks. This estimator turns your own figures into a simple rule: put X% of every payment aside, or £Y a month.

What it does

• Three inputs: your other income (wages or pension, before tax), what your side hustle brings in for the tax year, and your costs. A best guess is fine.

• £1,000 allowance or costs: works out your side profit both ways and uses the lower one (or the one you choose). You can only use one.

• Income Tax, with and without your side profit: band by band (20%, 40%, 45%), including the Personal Allowance taper above £100,000, so you see the EXTRA tax your side hustle adds.

• Class 4 National Insurance at 6% and 2%, plus a plain-English Class 2 line for the tax year (treated as paid, or voluntary).

• What to put aside: the estimated total, the % of each payment, a monthly pot and a weekly pot.

• Payments sheet: log each payment and see how much to move to your tax pot, then tick it off.

• Both tax years: switch between 2025-26 and 2026-27. Every rate sits on a Rates & Sources sheet with its GOV.UK link (checked 28 October 2026).

What's included

• Side-Hustle-Tax-Set-Aside-Estimator.xlsx: the blank estimator.

• Side-Hustle-Tax-Set-Aside-Estimator-EXAMPLE.xlsx: the same file with clearly labelled made-up figures.

• A Google Sheets guide.

Good to know

• Not tax advice and not an official HMRC calculator. The figures are ESTIMATES based on the assumptions listed in the file (for example: wages or pension as your only other income, no savings or dividend income, no other reliefs). HMRC works out what you actually owe from your Self Assessment return.

• Class 4 National Insurance is worked out without the Class 4 annual maximum, so if you also have high employment earnings the estimate can be too high.

• For England, Wales and Northern Ireland. Scottish taxpayers have different Income Tax bands: see our Scottish tracker instead.

• Student loan repayments and payments on account aren't included.

• Plain formulas only: no macros, no add-ons, no subscription.

• Refunds and cancellations: https://payhip.com/BootstrapSheets/refunds-and-cancellations (your statutory rights aren't affected).

• From Bootstrap Sheets: plain, UK-focused spreadsheets for side hustles and small budgets.