It depends entirely on your situation — your earnings, the tax you've paid, and the work expenses you've covered yourself.
As a guide:
A single year's claim often pays out hundreds of pounds.
Because you can claim up to 4 tax years at once, multi-year claims frequently run into the thousands.
The largest claims we've handled have exceeded £10,000. 💷
The honest answer is that nobody can promise a figure before checking your records — which is exactly what we do. Start your claim and once we've reviewed your HMRC records and expenses, you'll get a personal estimate to approve before anything is submitted. No refund, no fee.