Loan Calculator
Work out the monthly payment, total interest and total cost on any fixed-rate loan: personal, auto, or student. See how much you save by paying extra each month. Currency is a toggle, so the tool works whether your money is in pounds, dollars, or euros.
Explain like I'm 5 (what even is this calculator?)
You borrow some money and pay it back a little at a time, with interest on top. This tool tells you what the "a little at a time" works out to each month, how much interest you end up paying in total, and how much sooner you'd finish if you paid a bit extra each month.
Calculate
Enter your numbers, then press Calculate.
Summary
- Monthly payment–
- Loan term–
- Total interest–
- Total cost (principal + interest)–
Amortisation snapshot
- First payment: principal–
- First payment: interest–
- Last payment: principal–
- Last payment: interest–
With your extra payment
- New term–
- Months saved–
- Interest saved–
Prove it
Monthly payment uses the standard fixed-instalment formula M = P · r · (1 + r)n ÷ ((1 + r)n − 1), with P the loan amount, r the monthly rate (APR ÷ 12 ÷ 100), and n the term in months. First and last payment splits come from the amortisation identity: each month's interest = remaining balance × r; principal = monthly − interest. At 0% rate, the calculator just divides the loan amount by the number of months. The extra-payment projection simulates the loan month by month.
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What this calculator is actually doing
A fixed-rate loan with equal monthly payments follows one of the oldest formulas in consumer finance. You borrow a fixed amount, the lender charges interest on the balance each month, and you make the same payment every month until the balance hits zero. Early in the term, most of your payment goes to interest because the balance is high. Late in the term, most of it goes to principal because the balance is small. The monthly number stays the same but the mix inside it shifts.
That mix is what makes overpayments so powerful. An extra pound paid today takes a pound off the balance that would otherwise be earning the lender interest for months or years. The calculator shows the compounding effect: a small extra payment can shave a surprising number of months off the term.
Personal, auto, or student loan?
The maths is the same for all three, which is why one calculator covers them. The differences live in the context around the loan, not the formula.
Personal loans
Unsecured, fixed term, fixed rate. Usually two to seven years. The rate depends on your credit score and the loan amount. Most lenders allow overpayment without penalty, but check the agreement; some still charge an early-settlement fee on the interest you would have paid.
Auto loans
Secured against the car. The loan amount is the price of the car minus any deposit or trade-in value, plus sometimes extras like dealer-arranged GAP insurance rolled into the total. The rate and term are usually tighter than personal loans: three to six years is typical. A car depreciates faster than the loan balance falls in the early years, which is why it is possible to owe more on a car than it is worth.
Student loans
This is where the calculator's assumptions start to break. US private student loans and some older UK Plan loans behave like ordinary fixed-rate loans. US federal loans on income-driven repayment, and UK Plan 2 and later, do not: you pay a percentage of income above a threshold for a set number of years, and any remaining balance is written off. This tool is not accurate for those plans. Use your government's official repayment calculator instead.
The rule of overpayments
Before you set up an extra monthly payment, check two things. First, that your lender accepts overpayments without a penalty. Most do on personal and auto loans. Some mortgages and older loans charge an early-repayment fee that can undo the savings. Second, that overpaying the loan is a better use of the money than paying off a higher-interest debt elsewhere. If you have a credit card charging 24% and a loan charging 6%, the card always wins.
What this tool does not do
It does not include arrangement or early-repayment fees. It does not handle variable-rate loans or promotional-rate periods that change halfway through the term. It does not model income-driven student loan repayment. It assumes you make every payment on time, with no missed or deferred payments. For any of those, the lender's own statement is the only source of truth.
Nothing on this page is financial advice. For an actual loan, the lender's own quote is what matters.
Related calculators
Loans sit next to the rest of the household numbers.
Frequently asked questions
How do I calculate a loan's monthly payment?
The standard formula is M = P × r × (1 + r)n ÷ ((1 + r)n − 1), where P is the loan amount, r is the monthly rate (APR ÷ 12 ÷ 100), and n is the term in months. At 0%, monthly payment is simply the loan amount divided by the number of months.
Does paying extra each month really save me interest?
Yes. Every extra pound (or dollar, or euro) reduces the balance, and the balance is what interest is charged on. Even a small regular overpayment can shave months off the term. Check your agreement first to make sure the lender does not charge an early-repayment fee.
Is this tool accurate for student loans?
For fixed-rate, fixed-instalment student loans like US private loans and some older UK Plan loans, yes. For US federal income-driven plans and UK Plan 2 or later, no: those are income-based and work very differently. Use your government's own calculator for those.
Does this calculator send my numbers anywhere?
No. Everything runs in your browser. The numbers you type never leave your device.