Should You Repay Your Student Loan Early or Invest Instead?

Plan 2 Student Loan Mechanics

Plan 2 is the repayment plan for most graduates who started university in England or Wales from September 2012. Scottish graduates have Plan 4, and new English students from September 2023 have Plan 5. The mechanics of Plan 2:

• Repayment rate: 9% of income above the threshold (£28,470 in 2026/27). At £35,000/year income, you repay 9% x (£35,000 - £28,470) = £588/year (£49/month). At £50,000, you repay 9% x (£50,000 - £28,470) = £1,938/year (£162/month).
• Below threshold: Nothing. You pay £0 regardless of loan balance if your income is below £28,470. This automatic pause applies to unemployment, career breaks, and lower-income years.
• Interest: RPI + up to 3%. While your income is below £28,470, interest is RPI only. Between £28,470 and £49,130, interest is RPI + a proportion of 3% (pro-rated by income). Above £49,130, interest is RPI + 3%.
• Write-off: The entire outstanding balance — principal, accrued interest, everything — is cancelled 30 years after you first entered repayment (typically in April of the tax year after you graduated).

The write-off is unconditional. There is no means test, no upper income threshold, and no penalty. A graduate with £100,000 of outstanding balance at year 30 has it written off exactly the same as one with £5,000 outstanding.

Who Will Actually Repay in Full?

This is the central question. Research by the Institute for Fiscal Studies (IFS) consistently finds that only around 25-30% of Plan 2 graduates are expected to repay their full loan balance within 30 years. The remaining 70-75% will have some (often substantial) balance written off.

What determines whether you repay in full? The key factor is your lifetime earnings trajectory. To repay a typical Plan 2 loan of £45,000-£55,000 (including interest accumulation during 3-4 years of study) within 30 years, a graduate generally needs to sustain an income considerably above average throughout their working life. Based on IFS modelling, graduates who earn consistently above approximately £55,000-£60,000/year are in the range where full repayment within 30 years becomes likely.

For the majority — graduates who earn average or above-average but not high salaries, those who take career breaks, work part-time, or whose income grows slowly — the write-off at year 30 is the most likely outcome.

The Write-Off Probability: Why It Changes Everything

Once you understand that 70-75% of graduates will not repay in full, the financial logic becomes straightforward:

• If you are in the majority who will not repay in full: a voluntary overpayment reduces a balance that will eventually be written off. The effective return on that overpayment is zero (or negative in real terms, once the opportunity cost is accounted for). You have essentially paid debt that was going to be cancelled for free.
• If you are in the minority who will repay in full: voluntary overpayments reduce the balance and therefore the interest accruing, potentially saving money compared to waiting for the balance to compound at RPI+3%.

The challenge is that at the time of the decision (shortly after graduation), most people genuinely cannot be certain which group they will fall into. The appropriate response is probabilistic reasoning rather than certainty.

ISA vs Student Loan Overpayment

For a graduate who is (as most are) likely to have some balance written off, the comparison between investing in a stocks-and-shares ISA and making voluntary student loan overpayments looks like this:

The ISA wins on every dimension for graduates who will not repay in full. Even for graduates who might repay in full, the ISA's liquidity is a significant practical advantage: you can use ISA funds to make a large loan repayment later if you determine you are going to repay in full, but you cannot recover an overpayment made years earlier.

Pension vs Student Loan Overpayment

Pension contributions are even more compelling than ISA investment for most graduates with student loans, for three reasons:

1. Immediate tax relief: A basic-rate (20%) taxpayer who makes a £100 personal pension contribution effectively pays £80 (HMRC adds £20 tax relief). A higher-rate taxpayer claims back a further £20 through Self Assessment, paying only £60 net for £100 of pension contribution. The effective immediate return on a higher-rate pension contribution is 67% before any investment growth.

2. Employer matching: If your employer will match pension contributions you are not already making, every £1 you put into a pension is matched by £1 from your employer — a guaranteed 100% return before investment growth. This almost always beats any alternative use of that pound.

3. Student loan repayment reduction via salary sacrifice: Making pension contributions by salary sacrifice reduces your gross income, which in turn reduces your student loan repayments. At £40,000 income, a £5,000 salary sacrifice pension contribution saves 9% x £5,000 = £450/year in student loan repayments. This is an additional free benefit on top of NI savings and pension tax relief.

Worked Example: Three Graduates, One Decision

Assume three graduates, each with a £50,000 Plan 2 loan and £2,000/year of spare cash. They are deciding between ISA investment and voluntary loan overpayments:

• Graduate A (income grows to £38,000, stays there): Repays 9% x (£38,000 - £28,470) = £858/year. After 30 years, her total repayments are approximately £25,740 — well below the original £50,000 loan. Balance written off: approximately £40,000+ (with interest). ISA invested at 8%/year over 30 years: £2,000/year grows to approximately £244,000. Overpaying the loan would have repaid debt destined for write-off. Clear winner: ISA.
• Graduate B (income grows steadily to £65,000 by age 35): Likely to repay in full before year 30. For B, voluntary overpayments in early years when the RPI+3% interest is compounding quickly have genuine value — they reduce the balance before it becomes very large. The comparison with an ISA returning 8%/year is closer. Clear winner: depends on actual investment returns vs loan interest. Modelling needed.
• Graduate C (partner of Graduate A, goes part-time for a decade): Income below threshold for 10 years — no repayments at all in those years. Balance grows with RPI-only interest. Almost certainly in the write-off group. Clear winner: ISA.

Plan 5 vs Plan 2: Is the Logic Different?

Plan 5 applies to English students starting from September 2023. The key differences:

• Repayment threshold: £25,000 (lower than Plan 2's £28,470) — you start repaying at a lower income
• Write-off: 40 years (longer than Plan 2's 30 years)
• Interest: RPI only, with no +3% surcharge (lower than Plan 2)
• Graduate contribution: Plan 5 graduates are expected to contribute more to their loans on average than Plan 2 graduates, due to the lower threshold and longer repayment period

Despite this, IFS projections suggest the majority of Plan 5 graduates will still have some balance written off at 40 years. The same fundamental logic applies: for most graduates, overpayments are likely to reduce a balance destined for write-off. However, the proportion who will benefit from overpaying is higher under Plan 5 than Plan 2, because the longer write-off window and lower threshold mean more graduates will repay in full. High earners under Plan 5 should model their repayment trajectory carefully.

The Mortgage Application Consideration

Many graduates worry that their student loan affects their mortgage prospects. The facts:

• The loan balance does not appear on your credit file
• The monthly repayment does reduce your net take-home pay, and lenders factor this into affordability
• A £162/month repayment at £50,000 income might reduce the maximum mortgage by approximately £30,000-£50,000 depending on the lender and multiplier
• Overpaying the loan before a mortgage application slightly improves monthly income (the repayment drops or stops) but does not improve your credit score

If your goal is to maximise mortgage borrowing, building a larger deposit through ISA savings will almost always have a greater positive impact than reducing the student loan balance — since a larger deposit improves your LTV, reduces your mortgage rate, and directly increases purchase power.

The Verdict: Invest for Most, Evaluate for High Earners

Key Sources

• GOV.UK: Repaying Your Student Loan
• IFS: Higher Education Funding in England
• Student Finance England
• MoneyHelper: Student Loan Repayments