About Sidetally
Last updated: 11 August 2026
Sidetally exists because of one specific gap: almost every UK tax calculator assumes self-employment is your only income. Most people with a side hustle aren't in that position at all, they have a day job too, and that changes the maths in a way most tools simply don't account for.
Why this matters
If you're employed and also earning from a side hustle, your personal allowance is usually already used up by your salary. That means your side-hustle profit often gets taxed at your full marginal rate, with no tax-free slice at all, something a calculator built only for full-time self-employment will never show you. Sidetally was built specifically to close that gap: it takes your salary and your side-hustle profit together, and shows you what you actually keep once both are properly stacked.
What it does, and doesn't do
Sidetally is a single free calculator. You enter your salary and your side-hustle profit, and it shows your Income Tax, Class 4 National Insurance, and student loan repayment (if applicable), broken down in plain English rather than jargon.
Everything runs in your own browser. The figures you enter are never sent to any server, we don't see them, we don't store them, and there's no account to create. If you accept cookies, some anonymous analytics data may be collected to help understand how the site is used, that's covered in full in the Privacy Policy.
Where the numbers come from
Every rate and threshold in the calculator is taken directly from HMRC's and the Scottish Government's published figures for the current tax year, Income Tax bands, Class 4 National Insurance thresholds, the £1,000 trading allowance, and student loan repayment plans. The tool is rebuilt each April when new rates are confirmed. It's still an estimate, not a substitute for professional advice, and that caveat is deliberate: see the Terms & Disclaimer for the full detail on what Sidetally is and isn't.
Who's behind it
Sidetally is run by Kyle Manson, a UK sole trader. It's a genuinely small, independent project, not a product built by an accountancy firm or a fintech company, just an attempt to fix one specific, recurring gap in the tools already out there.
Get in touch
Questions, corrections, or something that doesn't look right? Email contact@sidetally.co.uk.