Guide

Should I invest or overpay my student loan?

One of the most common financial questions for UK graduates. The answer depends heavily on which loan plan you have, your salary, and whether your loan is on course to be written off.

The key question: will your loan be written off?

UK student loans are not like ordinary debt. If you haven't repaid in full by the end of your loan term (25–40 years depending on your plan), the remaining balance is written off by the government — and you owe nothing further.

This completely changes the overpayment calculation. If your loan is on track to be written off, every pound you overpay only reduces the written-off balance — it doesn't reduce what you actually pay over your lifetime. In that case, overpaying is effectively throwing money away.

If your loan will be paid off in full

In this case, overpaying does reduce your total repayments. The question becomes whether the interest you save on your loan is greater or less than the return you'd earn by investing the same money.

For Plan 2 borrowers on higher incomes, loan interest can be RPI + 3%. At recent inflation levels (RPI ~3–4%), that's an effective rate of 6–7%. This is high — it's harder for investment returns to beat it on a risk-adjusted basis.

For Plan 1 and Plan 4 borrowers, interest is capped at min(RPI, Bank Rate + 1%) — typically 3–4.5%. Lower rates shift the balance more towards investing.

What is index fund investing?

An index fund is a type of investment that tracks a broad market index — like the MSCI World (global equities) or the FTSE All-Share (UK stocks). Instead of picking individual companies, you own a tiny slice of hundreds or thousands of companies at once.

Index funds have historically outperformed most actively managed funds over the long run, largely because they have lower fees and because most fund managers can't consistently beat the market. They are the bedrock of passive investing.

These are real returns — after stripping out inflation. They smooth over individual years that can vary wildly (global equities have historically ranged from −40% to +50% in a single year). The long-run average only applies if you stay invested for 15–20+ years and don't panic-sell in downturns.

The risk profiles in the calculator

The calculator uses three simplified risk profiles:

Things the model doesn't capture

• –Tax efficiency: ISA wrapper eliminates capital gains and dividend tax, significantly boosting net returns.
• –Sequence of returns risk: getting big losses early in your investment horizon hurts much more than the same loss later.
• –Employer pension matching: if your employer matches pension contributions, that's an immediate 25–100% return — always prioritise this first.
• –Emergency fund: investing before having 3–6 months of expenses in cash is risky.
• –Salary changes: your income (and therefore loan repayments) will change over your career.

A simple decision framework