UK Plan 5 student loans behave like a graduate tax, not a normal debt. Repayment is 9% of income above £25,000, interest is RPI only, and the loan is written off after 40 years. The IFS projects that around 65% of Plan 5 borrowers will never repay in full — meaning voluntary overpayments to "clear" the loan have no benefit. Many graduates lose £15,000+ over their working life by treating Plan 5 as ordinary debt.
How Plan 5 actually works
Plan 5 applies to undergraduate loans for courses starting in England from 1 August 2023 onwards. Key features for 2026/27:
- Repayment threshold: £25,000/yr. No repayments below this. Earnings above are subject to 9% deduction.
- Repayment rate: 9% of earnings above £25,000.
- Interest: RPI only. No "RPI + up to 3%" graduate-supplement (which Plan 2 had).
- Write-off: 40 years after the first April after graduation.
- Collection: via PAYE for employees; via Self Assessment for self-employed.
The repayment threshold is frozen until April 2027, then expected to rise by RPI annually. Compare to Plan 2 (most current graduates): £27,295 threshold (frozen), 9% rate, RPI + up to 3% interest, 30-year write-off.
The 40-year write-off — why most won't repay
A typical Plan 5 graduate’s loan looks like:
- Tuition fees: 3 years × £9,535 = £28,605
- Maintenance loan: 3 years × £8,000 (typical) = £24,000
- Total borrowed: £52,605
- Interest accrued during study (RPI): ~£5,000
- Balance at graduation: ~£57,000
After 40 years at RPI interest (assume 3% RPI average), the balance compounds to about £180,000 if no repayments are made. Repayments of 9% above £25,000 over 40 years on a typical UK career income profile (£30k → £50k → £45k average) would total around £140,000-£160,000.
The IFS calculates that around 65% of Plan 5 borrowers will never repay in full within 40 years, even at competitive UK earnings. They’ll repay the 9% throughout their career and have remaining balance written off at year 40.
When voluntary overpayments help — and when they don't
Overpayments only help if you would otherwise have repaid the loan in full within 40 years AND you can clear the remaining balance before then.
So overpayments are sensible for:
- High-earning graduates likely to repay in full. If you’ll earn £70k+ for most of your career, the natural 9% repayments will clear the loan before year 40 — and the longer it’s outstanding, the more interest accrues. Overpaying saves total interest.
- Graduates approaching write-off who are still well below balance. If you’re 35 years in with £20k still owing and earning £80k, voluntary acceleration prevents the final 5 years of high repayments.
Overpayments are wasteful for:
- Most graduates earning under £45k for most of their career. The 9% deductions never quite catch the compounding interest. Loan will be written off. Overpayments just shift cash from your bank account to HMRC for no future benefit.
- Graduates with caring responsibilities or career breaks. Anything that reduces lifetime earnings makes write-off more likely.
- Graduates who haven’t maxed pension contributions. The 9% extra you’d overpay to the loan would, in a higher-rate-taxpayer’s pension, become £1.67 (with 40% relief) — a much better use of marginal capacity.
Worked comparison — £45k graduate, overpay vs invest
Scenario: £45,000 graduate, has £5,000 spare cash
Option A: Voluntary overpayment to student loan
- £5,000 goes to Student Loans Company
- Loan balance reduces by £5,000
- Future 9% deductions still continue (based on income, not balance)
- If loan would be written off anyway: £5,000 effectively donated to HMRC
- If loan would be cleared at year 30 anyway: saves ~£500 of interest. Modest benefit.
Option B: £5,000 into Stocks & Shares ISA at 5% real return
- £5,000 invested in global tracker
- After 25 years at 5% real: £16,932 in real terms
- Tax-free withdrawal at retirement
- 9% loan deductions continue as before (no overpayment, so the loan situation is unchanged)
Option C: £5,000 into SIPP at 5% real return (higher-rate taxpayer)
- £5,000 net pension contribution = £6,250 gross (basic rate added)
- Higher-rate relief claimed via SA = additional £1,250 refund
- Net cost to investor: £3,750
- £6,250 gross compounded 25 years at 5% real = £21,165
- 25% tax-free PCLS = £5,291 tax-free, rest taxed (typically at marginal rate)
- Net after tax: ~£16,000+
Pension wins materially because of the 40% relief on contribution. The student loan overpayment, by contrast, may have provided zero benefit.
The defensive playbook
What about Plan 2 (graduates 2012-2022)?
Plan 2 has different mechanics:
- Repayment threshold £27,295 (frozen until 2027)
- Interest at RPI + up to 3% (so much higher than Plan 5)
- 30-year write-off (vs 40 for Plan 5)
Plan 2 graduates have a much higher probability of repaying in full because the higher interest rate compounds debt faster. The IFS estimates around 25-30% of Plan 2 borrowers will repay in full — vs 65% who won’t for Plan 5.
For Plan 2 high-earners, voluntary overpayment is more often sensible than for Plan 5. But the maths still requires checking — and pension/ISA still usually win for tax-relief reasons.
Project your loan repayment trajectory
The student loan calculator handles Plan 1, 2, 4 and 5 — projecting total repayments and write-off probability at various income paths.
Open the student loan calculator →Sources and methodology
Plan 5 rules from gov.uk/repaying-your-student-loan/what-you-pay. IFS analysis at ifs.org.uk/publications. Student Loans Company guidance at gov.uk Student Loans Company.
UK Tax Drag is not authorised by the Financial Conduct Authority and does not provide regulated financial advice — see the content disclaimer for the full position. The methodology page documents how every calculator is built and reviewed.
Other tax traps deep dives
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- Tapered Annual Allowance deep dive
- HICBC deep dive (with 2024 reforms)
- Nursery-aged-child marginal rates up to 103%
- Second-job tax code trap
- Savings interest tax surprise
- Dividend tax stacking
- EIS clawback real-world cases
- VCT clawback real-world cases
- Salary sacrifice — loss of benefit trap
- Student loan Plan 5 overpayment trap
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