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Lumera in English
Financial calculators that run in your browser. Nothing to install, no account to create, and your figures never leave your device.
- Nothing to install
- No account needed
Available tools
More tools are on the way. If there is a calculation you keep doing by hand in a spreadsheet, it is probably a good candidate.
What you can work out here
The calculator answers two questions that most lenders leave vague. First, what a loan really costs you from start to finish — not just the monthly payment, but the total interest and any fees attached to it. Second, what changes if you pay more than the minimum: how many months earlier you would finish, and how much interest you would never pay.
It works for any fixed-rate loan repaid in equal instalments: mortgages, car loans, personal loans and student loans all use the same arithmetic. You can also line up to three scenarios side by side — a shorter term against a lower rate, for instance — and compare them by what they actually cost rather than by the payment that looks smallest.
How the numbers are worked out
Each month, interest is charged on the balance you still owe, and whatever is left of your payment reduces that balance. That is why the interest share of every payment is largest at the beginning and shrinks over time, and why an extra payment made early saves far more than the same amount paid years later: it goes straight to the balance, so every future interest charge is calculated on a smaller number.
One detail worth getting right: enter the loan's interest rate, not its APR. The APR already includes fees, so entering it alongside the fees would count them twice. The full method, the formula and the reference cases we check it against are set out in about Lumera and how we calculate.
Everything runs on your device
There is no account to create and nothing to upload. The amounts, rates and dates you type are processed by your own browser and are never sent to us — once the page has loaded you could disconnect from the internet and the calculator would still work. The site is funded by advertising, which is why you will see ads on the calculator pages, and the figures you enter play no part in that.
More calculators in Spanish
The Spanish section is further ahead and currently has five tools: amortisation with extra payments, early repayment (lower the payment or shorten the term), personal loan cost and APR, how much mortgage you can afford on your salary, and the snowball versus avalanche method for paying off several debts. If you read Spanish comfortably, they are all here — the maths is identical, only the language and the local rules differ.