Methodology: How Our Calculators Work

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 following primary sources:

• 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:

Interest is the lower of RPI or the Bank of England base rate plus 1% for Plan 1 and Plan 4; RPI alone, uncapped, for Plan 5; and slides from RPI to RPI plus 3% by income for Plan 2 and Postgraduate, subject to the 6% cap that took effect on 1 September 2026 for the 2026/27 academic year. Full detail, including the exact income bands the Plan 2 slide runs between, 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We do not publish figures we cannot trace to a primary source.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 often we check these figures

• Repayment thresholds: checked every November, after the Autumn Budget, and again each April when a new tax year starts.
• Interest rates: checked every March, when the ONS publishes the RPI figure that sets the rate, and again every September, when the new rate is applied to borrower accounts.
• Tuition fees and maintenance loans: checked every spring, when the Department for Education and GOV.UK publish the cap and maximums for the next academic year.
• Policy changes such as the Plan 2 threshold freeze, the 6% interest cap, or the Lifelong Learning Entitlement rollout are monitored continuously and applied as soon as they are confirmed, not just on the scheduled review dates above.

Every correction we make because of this checking process is logged, dated, on 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. Ours are:

• Threshold uprating: long-range projections use today's threshold held flat unless a calculator explicitly lets you set a different assumption. We do this because most thresholds are frozen for a fixed window (Plan 2 is frozen at £29,385 from April 2027 to April 2030, Plan 5 is frozen at £25,000 until April 2027) and because future upratings are not yet announced. A calculator that guessed at future upratings would be presenting a guess as a fact.
• Salary growth: our overpayment and payoff calculators default to 0% annual salary growth. This is a deliberately conservative, editable assumption, not a prediction that your salary will not rise. Any salary growth rate you enter changes the result significantly over long horizons.
• Interest compounding: our interest, overpayment and payoff calculators compound interest monthly on the outstanding balance, which matches how the Student Loans Company applies interest, and assume no missed or late repayments.
• Maintenance loan taper: our maintenance loan calculator interpolates in a straight line between the published maximum (household income £25,000 or less) and the published guaranteed minimum for each living arrangement, because GOV.UK does not publish a single formula, only a small table of examples. A self-check runs when the site is built and compares our calculated figures against every row GOV.UK has published, within £5 tolerance, and fails the build if a figure drifts.
• One plan at a time, by default: most calculators model a single loan plan. If you have more than one plan (for example an undergraduate Plan 2 loan and a Postgraduate loan), use our combined repayment calculator rather than adding the single-plan results together, since both loans are repaid simultaneously 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.
• 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.