Methodology: How Our Calculators Work
GOV.UK, MoneySavingExpert and Save the Student all publish some form of statement on how their student loan figures are produced. This page is ours. It sets out which constants our calculators use, where those figures come from, when they change, what our projections assume, and where those assumptions break down. If you think a figure is wrong, see how to report it at the bottom of this page.
Where our figures come from
Every rate, threshold and fee cap used in our calculators is stored in one central file in our codebase (student-loans.ts), not typed separately into each calculator. That file is checked against the primary sources below, which are also listed with the topic each one supports on our sources page:
- HMRC, Rates and thresholds for employers, for the annual, monthly and weekly repayment thresholds[source].
- GOV.UK, Repaying your student loan, for repayment rates, interest rates and write-off periods[source].
- GOV.UK, Student finance for undergraduates, for the tuition fee cap and maintenance loan maximums[source].
- GOV.UK, Student finance: how you're assessed and paid, for the means-test taper and payment schedule[source].
- The Office for National Statistics, for the RPI figure that sets Plan 1, Plan 2, Plan 4, Plan 5 and Postgraduate interest each March.
- Student Finance Wales, Student Finance NI and SAAS for the nation-specific tuition and threshold figures that differ from England.
- The House of Commons Library briefing on student loan interest rates and thresholds, for cross-checking and historical context[source].
Income tax bands, National Insurance thresholds and Scottish income tax bands used in our HMRC calculator suite are checked separately against GOV.UK and mygov.scot and stored in a second constants file (tax.ts).
The current constants, in one place
For the 2026/27 tax year, our calculators use:
| Plan | Threshold | Repayment rate | Write-off |
|---|---|---|---|
| Plan 1 | £26,900 | 900% | 25 years |
| Plan 2 | £29,385 | 900% | 30 years |
| Plan 4 (Scotland) | £33,795 | 900% | 30 years |
| Plan 5 | £25,000 | 900% | 40 years |
| Postgraduate | £21,000 | 600% | 30 years |
These figures are read from the same constants file the calculators use, so this table cannot disagree with them. The full per-plan working is in the next two sections, and the finder for your own plan is on our plan finder page.
We do not publish figures we cannot trace to a primary source. Where a number is uncertain, unannounced for a future year, or not independently verified, we leave it out rather than estimate it.
How each repayment is worked out
For every plan the rule is the same shape: you repay a fixed percentage of the income above your plan's threshold, and nothing if your income is at or below it. In symbols, repayment = rate × (income − threshold). For 2026/27:
| Plan | Yearly repayment in plain words | Example at £40,000 |
|---|---|---|
| Plan 1 | 900% of everything you earn over £26,900 | 900% × (£40,000 − £26,900) = £1,179 a year |
| Plan 2 | 900% of everything you earn over £29,385 | 900% × (£40,000 − £29,385) = £955 a year |
| Plan 4 (Scotland) | 900% of everything you earn over £33,795 | 900% × (£40,000 − £33,795) = £558 a year |
| Plan 5 | 900% of everything you earn over £25,000 | 900% × (£40,000 − £25,000) = £1,350 a year |
| Postgraduate | 600% of everything you earn over £21,000 | 600% × (£40,000 − £21,000) = £1,140 a year |
- Pay-period figures. Employers deduct per pay period, not once a year. HMRC publishes a monthly and a weekly threshold for each plan, each rounded down to a whole pound, and rounds each deduction down to a whole pound. Where a calculator shows a payslip figure it uses those published thresholds and that rounding, not the annual figure divided by 12 or 52.
- More than one loan. If you have an undergraduate loan and a Postgraduate Loan you repay both at once: the undergraduate rate over the undergraduate threshold and 6% over the Postgraduate threshold. Two undergraduate plans share the lowest threshold (GOV.UK).[source]
- Self Assessment. If you file a tax return, the year's repayment is worked out on your total income for the year, which can include income that payroll does not deduct from, such as dividends above £2,000.[source]
How interest is worked out
Interest is set each September from the previous March's RPI. For 1 September 2026 to 31 August 2027 RPI is 4.1%. Interest does not change how much you repay each month; it changes how big the balance gets.
| Plan | How the rate is set | Rate now |
|---|---|---|
| Plan 1 and Plan 4 | The lower of RPI or Bank of England base rate plus 1% | 4.1% |
| Plan 2 | RPI if income is £29,385 or less, rising on a straight-line scale to RPI plus 3% at £52,885 or more, capped at 6% for 2026/27 | 4.1% to 6% |
| Plan 5 | RPI only | 4.1% |
| Postgraduate | RPI plus 3% whatever your income, capped at 6% for 2026/27 | 6% |
The 6% cap applies to Plan 2 and Postgraduate loans for the 2026/27 academic year only. The calculators apply it to that year and no further, because no later extension has been announced[source]. The Bank of England base rate only matters for Plans 1 and 4, and only if it falls below 3.1%; the calculators default to 4%, which you can change.
How repayment start dates and write-off dates work
- Repayments start in the April after your course ends. A course that ends in 2022 means repayment starts in April 2023. Interest still builds up before then; nothing is repaid.
- Plan 5 cannot start before April 2026, however early the course ended, because the plan's first repayment year is 2026/27.
- The write-off clock starts at that April. Plan 1 is written off after 25 years, Plan 2, Plan 4 and Postgraduate after 30, Plan 5 after 40. A Plan 2 course that ended in 2022 is written off in April 2053.
- Age-65 rule. Plan 1 loans first taken out before 1 September 2006 are written off at age 65 rather than after 25 years. Our write-off checker applies this when you enter your year of birth.[source]
When these figures change
- Repayment thresholds: set by the government and normally take effect from April, the start of the tax year in which they are used for repayments.
- Interest rates: linked to the RPI inflation figure for March and reviewed each year from September.
- Tuition fees and maintenance loans: published by the Department for Education and GOV.UK for each academic year.
- Policy changes such as the Plan 2 threshold freeze, the 6% interest cap or the Lifelong Learning Entitlement take effect on the dates the government sets. Each page shows when it was last updated, and the footer shows the date of the most recent figure update.
Corrections to figures and wording are logged and dated on our corrections page and our change log.
What our calculators assume
A calculator that projects your loan forward five, ten or thirty years is not reporting a fact, it is running a model, and every model rests on assumptions. These are the ones the lifetime projection engine (the homepage calculator, the monthly repayment calculator and the total loan cost calculator) uses. They are assumptions, not published figures, and each calculator shows the values it used.
| Assumption | Value | What it does |
|---|---|---|
| Salary growth | 2.5% a year | Your pay rises by this each year. You can change it in the calculators that expose it. |
| Threshold uprating once a freeze ends | 2% a year | Plan 2 is frozen at £29,385 for the tax years starting April 2027, 2028 and 2029, then uprated from April 2030. Plan 5 stays at £25,000 until April 2027, then is uprated. Plan 1 and Plan 4 are uprated each April from the latest published figure (Plan 1 is published at £28,005 from April 2027). Postgraduate has no announced freeze, so it is uprated too. |
| RPI after the current rate period | 3% a year | The published 4.1% applies to 1 September 2026 to 31 August 2027 only. Interest for every later year uses this long-run figure. |
| Price inflation for "in today's money" | 3% a year | Used only to express future totals in today's pounds. It is set equal to the RPI assumption so the two agree. |
| Monthly maths | Monthly | Interest compounds monthly and repayments are made monthly, which matches how the loan account runs. The projection spreads the annual repayment evenly over twelve months; use the pay-period figures above for a payslip. |
Why thresholds use 2% but interest uses 3%. The threshold assumption is earnings growth (2%); the interest assumption is RPI (3%). They are separate inputs in the code, so they differ. GOV.UK's published Plan 1 rise for April 2027 (£26,900 to £28,005) is 4.1%, the same as March RPI, and the House of Commons Library says Plan 5 thresholds are intended to rise with RPI from April 2027. If thresholds rise faster than the 2% we assume, the repayments you would make are lower than our projections show. We have kept 2% because no figure is published beyond the Plan 1 rise; treat long projections as illustrations of the mechanics, not forecasts.
Overpayment and early payoff calculators. These run a simpler monthly simulation and hold your threshold flat. The overpayment calculator defaults to 0% salary growth, a deliberately conservative setting you can change, so the effect of an overpayment is not mixed up with an assumed pay rise; the early payoff calculator holds your salary flat. For Plan 2 and the Postgraduate Loan the early payoff calculator uses the highest current rate (6%) whatever your income, so for a lower-paid Plan 2 borrower it can overstate interest.
- Maintenance loan taper: the maintenance loan calculator interpolates in a straight line between the published maximum (household income £25,000 or less) and the published minimum for each living arrangement, because GOV.UK does not publish a single formula, only a table of examples. An automated test compares our figures with every row GOV.UK has published, within £5, and fails if a figure drifts.
- One plan at a time, by default: most calculators model a single loan plan. If you have an undergraduate loan and a Postgraduate Loan, use our combined repayment calculator rather than adding the single-plan results together, since both loans are repaid at once against the same salary.
Limitations
Our calculators are planning tools, not a substitute for your actual Student Loans Company statement or for regulated financial advice. In particular:
- We do not know your actual SLC balance, payment history or arrears. Figures are estimates from the inputs you provide, not a read of your account.
- Long-range projections (ten years or more) are more sensitive to the salary growth and threshold assumptions above than short-range ones. Treat a thirty-year total-cost projection as an illustration of the mechanics, not a forecast.
- Some figures we deliberately do not calculate or restate because we cannot independently verify them, including certain overseas repayment thresholds outside the published table and any Lifelong Learning Entitlement detail not yet confirmed by the Department for Education.
- What the calculators do not model. Month-to-month changes in pay, career breaks, and income outside the salary you enter. The lifetime projection does not apply the age-65 write-off rule for older Plan 1 loans (our write-off checker does), and our combined calculator handles one undergraduate plan plus a Postgraduate Loan, not two undergraduate plans at once.
- We are not regulated to give financial advice, and nothing on this site should be read as a personal recommendation. For advice specific to your circumstances, speak to a regulated financial adviser or the Student Loans Company directly.
Found an error?
Tell us. Every genuine correction we make is recorded, with the date and what changed, on our change log. If a figure on this site does not match what GOV.UK, the Student Loans Company, HMRC or your own SLC statement says, please contact us with the page and the figure in question and we will check it. The list of corrections we have already made is on our corrections page; the primary sources behind our figures are on our sources page, and how the site is edited is on our editorial policy.