Quick answer
Student loan repayments are usually based on income above the relevant plan threshold, not on the whole salary.
A salary calculator needs the correct plan because Plan 1, Plan 2, Plan 4, Plan 5 and postgraduate loans use different thresholds or rates.
Worked example: £35,000 salary with a student loan
A £35,000 salary may trigger student loan repayments if the selected plan threshold is below that income.
The calculator estimates the repayment using the plan selected in the form, then subtracts it from take-home pay alongside income tax, employee NI and pension deductions.
If you choose the wrong plan, the estimated monthly take-home pay can be materially wrong.
How payroll handles repayments
For employees, student loan repayments are usually deducted through payroll when earnings for the period are above the relevant threshold.
Bonuses and overtime can increase repayments in the pay period because payroll looks at pay for that period.
If you have more than one loan type, such as an undergraduate plan and a postgraduate loan, repayments can interact differently from a single-plan estimate.
Common mistakes
Choosing Plan 2 because it sounds familiar without checking the actual plan on Student Loans Company or HMRC records.
Assuming pension contributions always reduce student loan repayments. Treatment can depend on payroll and pension arrangement.
Forgetting that bonuses can increase deductions in a single month even if annual salary is unchanged.
Try the calculator
Use the related calculator to test the numbers against your own assumptions.
UK Salary CalculatorDisclaimer
This guide is an estimate-only explanation. Check Student Loans Company, HMRC or payroll records for your exact plan and repayment position.