Calculator methodology

The calculator projects a monthly repayment schedule from your remaining balance and current salary. It estimates mandatory repayments, interest added to the balance, total amounts paid, optional voluntary overpayments on the undergraduate plan, and whether the balance is cleared or written off within the modelled term.

Results are illustrative estimates for planning and comparison. They are not personalised financial advice, and they are not an official statement from the Student Loans Company or GOV.UK.

Undergraduate plans you can model: Plan 1, Plan 2, Plan 4 (Scotland/SAAS) and Plan 5. You can optionally add an England/Wales Postgraduate Loan alongside Plan 1, Plan 2 or Plan 5. The postgraduate product is modelled separately from your undergraduate plan. Plan 4 does not offer that England/Wales postgraduate toggle in this tool.

For plan-specific rules in plain English, see the student loan guides.

Core inputs:

• Undergraduate plan selection
• Year you finished university (used for repayment start and write-off timing)
• Current annual salary before tax
• Remaining undergraduate loan balance
• Optional England/Wales postgraduate balance and settings

Advanced settings let you change the repayment threshold, repayment rate, base interest assumptions, salary growth (realistic projection mode), and monthly voluntary overpayment on the undergraduate plan. Defaults come from the verified rule snapshot unless you change them.

The live engine converts annual salary to a monthly amount by dividing by 12. The monthly repayment threshold is the official PAYE monthly figure from the verified snapshot when the plan's default annual threshold is selected. If you customise the annual threshold, that custom figure is divided by 12 instead. If monthly income is at or below the monthly threshold, the mandatory repayment is £0. Otherwise the mandatory repayment is the repayment rate applied to the amount above that monthly threshold (9% for undergraduate plans; 6% for the England/Wales Postgraduate Loan at the verified defaults).

Before the April repayment-start date implied by the graduation year you enter, mandatory repayments are treated as £0 even if salary is above the threshold.

Each projection is anchored to the first day of the current calendar month, not to graduation. The first simulated monthly interest and repayment entry is one month after that anchor. Within each simulated year, salary is held constant. If salary growth is enabled, salary steps up once per completed year of the projection.

In simple (flat salary) mode, growth is forced to zero. In realistic mode, the annual growth rate you set is applied. The What-If salary slider always compares mandatory undergraduate repayments only: no overpayment and no salary growth.

Interest is applied monthly on the outstanding balance before that month's payment is deducted. The monthly rate is the resolved annual rate divided by 12.

Annual rates follow the selected plan rules at the verified snapshot: Plan 5 uses base RPI; Plan 1 and Plan 4 use the lower of RPI or Bank Rate plus the plan margin; Plan 2 uses an income-tiered rate between RPI and RPI plus 3% after study; the postgraduate product uses the total annual interest rate supplied for that product (the verified default is a fixed total rate for the pinned academic-year window). Caps encoded for later academic years only apply when the verified snapshot points at those later rules.

Salary growth only affects the projection when realistic mode is selected. Voluntary overpayments are added to the undergraduate plan's mandatory repayment each month and cannot exceed the remaining balance. The postgraduate simulation does not currently model voluntary overpayments.

Repayment start is represented as 6 April after the tax year of the graduation year you enter. Write-off is modelled as 5 April after the plan's write-off period from that repayment start: 25 years for Plan 1, 30 years for Plan 2, Plan 4 and postgraduate, and 40 years for Plan 5 in this engine.

Simulation dates normally fall on the first day of each month. The month containing 6 April is modelled as the first repaying month; projections remain anchored to the first of the current month with the first simulated entry one month later.

If the balance reaches zero first, the loan is treated as fully repaid on that month. If the write-off date arrives first, any remaining balance is treated as written off.

When both products are active, each loan is simulated separately with the same salary and graduation year, then display totals combine monthly repayments, amounts paid and interest. The headline payoff or write-off timing follows the loan that ends later. Product-level outcomes are only shown for balances you actually enter.

Official repayment, interest and related rules are centralised in a typed student loan rules layer and versioned by tax year (repayment) or academic year (interest). The live calculator uses a pinned verified snapshot for repayment tax year 2026/27, checked as of 11 July 2026.

Default projections hold the currently selected threshold, rate and interest assumptions constant for the whole forecast unless you change advanced forecasting settings. The tool does not automatically uprate thresholds or refresh RPI or Bank Rate during a projection.

Important limitations visible in the current implementation:

• Plan 1 write-off is approximated as the newer cohort rule (25 years after the April repayment start). Loans whose first payment was before 1 September 2006 are written off at age 65, and that older cohort is not modelled here.
• Plan 4 write-off is approximated for the post-1 August 2007 cohort (30 years). Older Scottish cohorts that can use age 65 or 30 years, whichever comes first, are not modelled.
• Cohort write-off policy exists in the rules registry, but the live engine still uses these legacy approximate dates based on graduation year.
• Official monthly PAYE thresholds are used when the plan's default annual threshold is selected; a customised annual threshold is divided by 12.
• The projection is anchored to the first day of the current month, with the first simulated monthly entry one month later. The month containing 6 April is modelled as the first repaying month.
• Projections do not model a full pre-repayment study interest phase from graduation.
• Payslip take-home estimates use England/Wales tax assumptions and are not offered for Plan 4 Scottish income tax.
• Inclusion of an official source in the registry does not mean every page or projection uses every source.

When official rules change, updates should be encoded in the central rules layer, re-verified against primary sources, covered by tests, and only then pinned into the live calculator snapshot. Advancing the verified "as of" date is a deliberate review step, not an automatic calendar rollover.

Future intention only: broader monitoring of official publications. Today the site does not automatically watch GOV.UK or other sources, does not auto-update live calculations, and does not guarantee that every projection matches your Student Loans Company account.

See the sources page for the citations behind the current verified snapshot, or open the calculator to run an estimate.