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Student loans — why it isn’t really a debt

Plan 1, 2, 4, 5 and postgraduate loans explained — the 9% graduate tax in disguise, and the honest maths of whether to pay it off early.

The name is the problem

A UK student loan has almost none of the properties of a debt. Repayments depend on your income, not your balance — earn below the threshold and you pay nothing, with no arrears, no default, no letters. It never appears on your credit file. Nobody chases the shortfall if you never clear it. And after a fixed number of years the whole thing is written off, whatever is left — £2,000 or £80,000, same outcome.

What it actually behaves like is a 9-percentage-point payroll tax on income above a threshold, with a sunset date. Once you see it that way, most of the anxiety — and most of the “should I pay it off?” question — resolves into ordinary tax planning. The balance and the scary interest letters matter far less than people assume; for many borrowers they are effectively fiction, because the write-off will arrive before the balance ever would have been cleared.

That’s the framing. The honest caveat: the terms are set by government, not contract, and governments have changed them before (the Plan 2 threshold was frozen for years, which is a stealth rate rise). “It’s a tax” cuts both ways — taxes can go up.

Which plan are you on?

Your plan depends on where you lived when you applied and when your course started. Repayment is 9% of pay above your plan’s threshold for undergraduate loans, deducted through payroll like tax:

Plan Who Threshold* Interest Written off
Plan 1 England/Wales, started before Sept 2012; all Northern Ireland £26,065 Lower of RPI and Bank rate + 1% 25 years after the April you were first due to repay
Plan 2 England/Wales, Sept 2012 – July 2023 £28,470 RPI to RPI + 3%, rising with income 30 years
Plan 4 Scotland £32,745 Same as Plan 1 30 years
Plan 5 England, from Aug 2023 £25,000 RPI only 40 years
Postgraduate England/Wales masters & doctoral loans £21,000, at 6% RPI + 3% 30 years

*The April 2025 confirmed thresholds, matching the marginal tax calculator; Plans 1, 2 and 4 rise each April (Plan 5 and postgraduate are frozen until 2027) — check gov.uk for the current figures. Scottish postgraduate borrowing sits inside Plan 4 rather than getting its own 6% band.

A postgraduate loan stacks on top of an undergraduate one: a Plan 2 + postgrad borrower repays 9% + 6% = 15% of pay above the respective thresholds. If you hold two undergraduate plans, the total is still 9%, split between them. Repayments start the April after you leave your course, and only in pay periods where you earn above the (monthly) threshold.

What it does to your marginal rate

Because repayment is a percentage of income above a threshold, it adds straight onto your marginal tax rate:

This is why graduates are the biggest winners from salary sacrifice: every £1 sacrificed into a pension skips income tax, NI and the 9%. A higher-rate Plan 2 graduate gives up just 49p of take-home per £1 of pension. Yes, lower repayments mean the loan lingers longer — but if you’re heading for write-off anyway (see below), that’s not a cost at all; the 9% was money you were never getting back either way. Run your own numbers in the marginal tax calculator, which models every plan and the stacking.

Should I pay it off early?

This is really one question: will you clear the balance before the write-off date anyway? Everything follows from the answer.

Probably never going to clear it → don’t pay a penny extra. This is most Plan 2 borrowers: typical balances of £45,000–£60,000, interest at RPI+, and a 30-year clock. If the write-off is coming, every voluntary overpayment is a pure donation to the Treasury — it reduces a balance that was going to be cancelled regardless, and changes your monthly repayments by exactly nothing (they’re set by income, remember). The interest rate is irrelevant to you: growth in a balance you’ll never repay costs you nothing.

Definitely going to clear it → it’s a real debt; now compare rates. High earners with smaller balances (many Plan 1 borrowers, and Plan 5’s 40-year term means far more of that cohort repays in full) will pay off the whole thing plus interest. For them, overpaying “earns” the loan’s interest rate, risk-free. But note what that rate is: Plan 1, 4 and 5 interest is roughly RPI or capped near the Bank rate — often beatable in a savings account, and almost certainly beatable by pension contributions given the relief above. Even a definite repayer is rarely in a hurry; money kept in your own account keeps its options.

Not sure → wait, because overpayments are irreversible. A career break, part-time years, moving abroad, retraining, redundancy — any of these can turn “definite repayer” into “write-off case”, at which point money already sent to the SLC is gone. Keeping the cash means you can always pay it off later; paying it off means you can never get it back. Uncertainty is an argument for doing nothing, and doing nothing is free.

The sometimes-yes cases. A small remaining balance you’ll clear within a couple of years anyway (especially on Plan 2’s RPI+3%); a high, stable income with pension and ISA allowances already well used; or wanting the monthly deduction gone for mortgage affordability — lenders count the repayment in what you can borrow, though the loan itself never touches your credit score. These are real, minority cases — the site’s summary is honest: usually no, sometimes yes.

And the ordering test any overpayment must pass first: expensive real debt cleared, emergency fund full, employer pension match taken, and a serious look at whether the same pound does more in a pension or ISA. For a probable write-off case, it isn’t a close contest.

Three admin traps worth knowing

Self-employed? Same 9%, collected annually through Self Assessment instead of payroll.

The one-line summary

Treat it as a 9% graduate tax with an expiry date, not a debt: if the write-off is coming, overpaying is a donation; if you’ll clearly repay in full, it’s a cheap debt that still usually loses to pensions and savings — and if you’re not sure, keeping the money is the option that stays reversible.

Last reviewed: August 2026.