Student Loan Calculator
Enter your remaining loan balance, interest rate, and the monthly amount you can pay — the calculator returns payoff time, total interest, and how much you save by adding an extra fixed amount each month. Works for US federal/private and UK Plan-style loans on the repayment side.
Time to payoff
10 yr
- Total paid
- £40,908.83
- Total interest
- £10,908.83
- Time saved by extra payment
- —
- Interest saved by extra payment
- £0.00
Each month, interest accrues on the remaining balance (APR ÷ 12). Your payment first covers that interest; whatever's left chips away at the principal. A higher monthly payment leaves more for principal, so the balance falls faster and accrues less interest in every subsequent month — the saving compounds over the life of the loan.
How to use this calculator
Enter your current loan balance — for US borrowers, check your loan servicer's dashboard (Mohela, Nelnet, Aidvantage etc.) or studentaid.gov; for UK borrowers, sign in to your Student Loans Company account. Use the annual interest rate (APR) — US federal undergraduate Direct Loans first disbursed July 2024 to June 2025 carry 6.53%; UK Plan 2 (post-September 2012, England/Wales) is currently capped at RPI + up to 3%; UK Plan 5 (post-August 2023) is RPI only. Enter the monthly payment you actually make (not the minimum the servicer prints — actual amount, including any auto-debit discount). Then add an optional extra monthly payment to see how much faster the loan clears. The result panel shows time to payoff (years + months), total amount paid, total interest, and the time and interest you save versus paying only the base amount.
How the calculation works
A fixed-rate student loan amortises like any other instalment loan. Each month the balance accrues interest at APR ÷ 12; your payment first covers that interest, then whatever is left reduces the principal. Smaller balance next month → less interest accrues → more of next month's payment goes to principal. The closed-form for months-to-payoff is k = −log(1 − B·r ÷ P) ÷ log(1+r), with B the balance, r the monthly rate, and P the monthly payment (including any extra). With r = 0 it collapses to k = B ÷ P. If P ≤ B·r, the payment cannot even cover the interest charge and the loan never amortises — the calculator flags that explicitly. Extra payments compound the saving: every dollar (or pound) you put toward principal today saves you all the interest that dollar would have accrued for the rest of the loan term.
Worked example
A $30,000 US federal undergraduate balance at 6.5% APR with $340/month → loan clears in about 10 years 0 months (120 months — this is essentially the Standard 10-year Federal repayment level payment), total paid $40,910, total interest $10,910. Adding $50/month extra (so $390/month) drops the payoff to about 8 years 4 months (100 months), total paid $38,910, total interest $8,910 — saving roughly 1 year 8 months and ~$2,000 of interest by paying $50 more per month. UK Plan 2 example: £40,000 balance at 7.7% (RPI 4.7% + 3% margin, capped) with £350/month → about 17 years 3 months to clear the balance voluntarily, total interest £32,330. (UK Plan loans are statutorily written off after 30 or 40 years depending on plan; many borrowers never repay in full. This calculator models the "clear it before write-off" path — see the FAQ for write-off considerations.)
Frequently asked questions
Does this work for US and UK student loans?
Yes for the underlying amortisation maths — given a balance, APR, and a fixed monthly payment, the time to pay off and total interest are identical whether the currency is USD or GBP. The complications it does not model are jurisdiction-specific: US income-driven repayment plans (SAVE, PAYE, IBR, ICR) whose monthly payment varies with income, UK Plan 1/2/4/5/Postgrad income-contingent repayment that takes a percentage of earnings above a threshold and writes off the balance after 25/30/40 years, capitalised interest events (US: end of grace period, deferment, forbearance; UK: balance grows continuously), and Public Service Loan Forgiveness (PSLF). For income-driven UK borrowers under Plan 2, monthly repayments are 9% of earnings above £27,295 (2024/25) regardless of balance — the "what will I actually pay each month" question is income-driven, not balance-driven. Use this calculator when you are on a fixed repayment schedule, or to model paying off the loan voluntarily before write-off.
What APR should I use?
US federal Direct Loans set the rate at first disbursement and it is fixed for the life of the loan: 2024–25 undergraduate Subsidised/Unsubsidised 6.53%, graduate Unsubsidised 8.08%, Direct PLUS 9.08% (source: studentaid.gov). Older loans have lower fixed rates — check your servicer for the exact APR on each loan if you have several. US private loans are usually fixed or floating LIBOR/SOFR-linked — use the current APR your lender quotes. UK Plan 2 is RPI + 0% to 3% sliding with income (max 3% during study and for the first year after course end if salary above the upper threshold) — currently capped because of the "prevailing market rate" cap; check the Student Loans Company site for the current applicable rate. UK Plan 5 (post-Aug 2023, England) is RPI only. UK Plan 4 (Scotland) and Plan 1 (older) are RPI or BoE base + 1%, whichever is lower.
Should I make extra payments on my student loan?
Maths-only answer: every extra dollar/pound paid to principal earns a guaranteed risk-free return equal to your loan APR — at 6.5% that's better than most savings accounts and competitive with stock-market expectations after tax. But the maths is not the whole picture. (1) US federal borrowers: if you are pursuing PSLF or could be eligible for IDR forgiveness, do not voluntarily prepay — you'd be paying down a loan that would otherwise be forgiven. (2) UK Plan 2/4/5 borrowers: if your career trajectory means you will not clear the loan before the 30/40-year write-off, every voluntary repayment is money you would not otherwise have paid. The break-even depends on your projected lifetime earnings. The Money Saving Expert "should I repay my student loan early" tool walks through this in detail. (3) Both jurisdictions: keep an emergency fund and clear higher-rate debt (credit cards, car loans) before overpaying student loans.
Why does the calculator say "payment too small"?
It means your monthly payment is less than (or equal to) the monthly interest the loan accrues. At a 7% APR on a $50,000 balance, monthly interest is $50,000 × 0.07 ÷ 12 ≈ $292 — so any payment of $292 or less keeps the balance flat (or growing). The principal never reduces, the loan amortisation formula divides by zero, and the loan would in theory never be paid off. In practice US private and federal-Standard plans require a payment at least equal to interest plus a small principal amount; this calculator is for "what if I pay X" scenarios, so it will flag rather than silently return Infinity. UK Plan loans operate differently — the SLC takes the income-contingent payment regardless of whether it covers interest, and any shortfall just grows the balance until write-off.
How does this differ from your amortisation calculator?
The amortisation calculator takes a loan term in years (e.g. 30) and works backward to find the level monthly payment. The student loan calculator takes the monthly payment as input and works forward to find the term — which matches how most borrowers think about student loans ("I pay $X a month, how long until it's gone?"). The student loan calculator also models an extra-payment overlay so you can see the time/interest impact of paying $20, $50, or $100 more per month — useful when deciding whether to set up automatic extra payments or apply a tax refund / bonus directly to principal.
What about variable-rate UK student loans where interest changes annually?
UK Plan 2 and Plan 5 interest rates are reset at least annually (in September) based on the previous March RPI. This calculator uses a single fixed APR — a snapshot — so it cannot project the exact future trajectory. Two reasonable approaches: (a) use the current applicable rate to estimate the worst-case interest for the next 12 months, then recompute at the next rate change; or (b) use the long-run RPI assumption (the OBR uses 2–3% in long-run forecasts) plus the appropriate margin. For Plan 2 with income above the upper threshold and a long horizon, RPI + 3% (currently capped) is a fair worst-case planning number. Remember that for income-driven plans the monthly payment is set by income, not the APR — the APR only affects how fast the balance grows between today and write-off.