About Overpay or Invest
Who runs it
I’m a UK citizen living in Australia, and I have a UK student loan of my own that I’ve been trying to get on top of. This site started with a question I couldn’t get a straight answer to: is it worth overpaying, or better to invest? The calculator is my attempt to answer it, and the guides set out what the rules are, checked against GOV.UK.
Overpay or Invest is an independent project. It is general information, not financial advice, and it is not affiliated with the Student Loans Company, the UK government or any lender.
What it does
Overpay or Invest is a free calculator for people in the UK with a student loan. It helps you compare two choices: putting extra money towards your loan, or keeping to the minimum repayments and investing the difference instead.
Why it exists
For many UK borrowers, the loan is written off before it is fully repaid. When that is true, paying extra can just hand money to the loan company that would have been cancelled anyway. For others, the loan will be cleared and the interest really does cost money. Which case you are in depends on your plan, your salary and when you started repaying. The calculator works that out from your own numbers.
How it works
Each plan year you repay a fixed share of your income above your plan’s threshold, whatever your balance is. Whatever is left is written off a set number of years after the April you first started repaying. The calculator runs that year by year, once with minimum payments only and once with your overpayment, and compares the result with investing the same money at the return you choose.
- Covers Plan 1, Plan 2, Plan 4 (Scotland), Plan 5 and the Postgraduate Loan.
- Uses the 2026–27 thresholds and interest rates.
- Everything is calculated in your browser. The figures you type in are not sent to us. See the privacy policy.
Where the rules come from
Plan rules are taken from gov.uk and the House of Commons Library briefing on student loan repayment (CBP-10654). Thresholds and rates change, so please check your own figures against your loan statement.
How we keep the figures accurate
- One source of truth. Every threshold, repayment rate, interest rate and write-off period used by the calculator and quoted in the guides comes from a single data file, so the site can’t contradict itself. When a figure changes, it is changed in one place.
- A monthly check. Once a month an automated check reads the official GOV.UK repayment page and confirms that each of those figures still appears there, and whether GOV.UK mentions a newer tax year. If something doesn’t match, it flags it for a person to look at. Nothing on the site changes automatically.
- What the check does not cover. It checks the figures, not every sentence in every guide. Guides are written from GOV.UK and Student Loans Company guidance and show the date they were last updated. Where a guide and GOV.UK disagree, GOV.UK is right, and we’d like to hear about it.
- When things change. Repayment thresholds normally change on 6 April and interest rates are usually reset on 1 September. We aim to update the site soon after each change.
How AI is used
I use an AI assistant (Claude, made by Anthropic) to help write the guides and to build the calculator and this site. The guides are checked against GOV.UK’s own pages, and the figures are checked against GOV.UK automatically every month (see above). AI can still get things wrong, which is why GOV.UK is always the source to trust if the two ever differ, and why I’d like to hear about any mistake you spot.
Limits
It is an annual approximation of a monthly system, so it is directionally useful rather than exact to the penny. It models one loan at a time and assumes steady salary growth. Please read the disclaimer: this is general information, not financial advice.
Spotted a mistake?
If a threshold, rate or result looks wrong, please tell us at hello@overpayorinvest.com. Corrections are welcome and we will check them against official sources.