How do I keep records for a side income?

Side income becomes stressful at the point where you have to work out, retrospectively, what happened. Keeping the record as you go removes that entirely.

Safety

Step by step

1. Separate it from your personal money.A second current account, or a dedicated pot. Everything relating to the side income goes through it. This one decision makes every later step straightforward.
2. Record income as it arrives.Date, who from, amount, what for. A spreadsheet is entirely sufficient — this does not need software until it is genuinely a business.
3. Record costs in the same place.Date, supplier, amount, what it was for. Materials, fees, mileage, equipment. Missing costs means overstating profit, which is your own money lost.
4. Keep the evidence, not just the number.Photograph paper receipts immediately and file digital ones into a folder per tax year. Thermal receipts fade to blank within months.
5. Set a monthly slot.Half an hour, same time each month. Download the statement, tick everything off, file the receipts. That habit is the whole system.
6. Note the mixed-use items carefully.A phone, a car, a room used partly for the work. Record the proportion and how you arrived at it at the time. A reasoned note written contemporaneously is worth a great deal.
7. Track mileage as you go.Date, journey, purpose, miles. It is impossible to reconstruct later and it is frequently one of the larger allowable costs.
8. Set money aside for tax from the start.A proportion of every payment into a separate pot, from the first one. The bill arrives long after the money has been spent otherwise.
9. Check the current thresholds on GOV.UK.There is a trading allowance below which income need not be declared, and registration deadlines that follow the tax year. Both change, so check rather than rely on what someone told you.
10. Know your tax year dates.The UK tax year runs to early April, and the self assessment deadline is the following January. Filing early does not mean paying early, and it removes the January scramble entirely.
11. Keep records for as long as required.Several years, and longer for some circumstances. Check the current requirement — it is longer than most people assume.
12. Back it up.Cloud storage plus one other copy. A spreadsheet on one laptop is a single point of failure for several years of records.
13. Keep client and platform records too.Invoices, platform statements, contracts. Online platforms increasingly report earnings directly, so your figures should match theirs.
14. Get advice once it is material.An accountant for a straightforward side income is inexpensive relative to what a mistake costs, and they will tell you what you are missing.

Tips

• Separate account first. Everything else becomes easy once the money is not mixed in with your own.
• Photograph paper receipts on the day. Thermal paper goes blank within months.
• Put money aside for tax from the first payment, not when the bill arrives.

Common mistakes

• Leaving it all until the deadline — Reconstructing a year from memory and bank statements takes far longer, misses allowable costs, and produces a figure you cannot properly evidence.
• Not setting tax money aside — The bill can arrive many months after the income, by which point it has been spent, and that is the commonest cause of side-income stress.

If it doesn't work