What is a loan and amortization calculator?
A loan calculator lets you know, before signing, how much you’ll pay each month, how much of that payment is interest and how much actually reduces your debt. It also generates the amortization schedule: the month-by-month breakdown of principal repaid, interest paid and outstanding balance.
This tool covers the three main systems used in banking and finance:
| System | Payment | Principal Repayment | Interest | Typical Use |
|---|---|---|---|---|
| French | Constant | Grows each month | Decreases each month | Mortgages, personal loans, car (Spain, Europe, LatAm) |
| German | Decreasing | Constant | Decreases each month | Business loans, some Nordic countries |
| American | Interest-only (constant) | Zero until end | Constant | Bridge loans, bonds, corporate operations |
How each system works
French System (fixed payment) — The Standard
This is the most widespread for mortgages and consumer loans in Spain. The monthly payment doesn’t change throughout the loan, but its composition does:
- At the start: most of the payment is interest, little principal
- At the end: most is principal, almost no interest
The monthly payment formula:
Payment = (P × i) / (1 - (1 + i)^(-n))
Where:
- $P$ = Initial principal
- $i$ = Monthly interest rate (annual / 12)
- $n$ = Total number of payments (years × 12)
Example: €150,000 at 3.5% for 30 years → Payment €673.57. Total paid: €242,485. Interest: €92,485.
German System (constant principal repayment)
Here you repay the same amount of principal each month. The payment starts higher and decreases progressively because interest is calculated on a linearly decreasing balance.
- Month 1 payment = (Principal / n) + (Principal × i)
- Month n payment = (Principal / n) + ((Principal / n) × i)
Advantage: You pay less total interest than French system. Disadvantage: Initial payment is higher, reducing borrowing capacity.
American System (interest-only)
You only pay interest during the loan term. At maturity, you repay all principal at once.
- Monthly payment = Principal × i (constant)
- At end: final payment = Principal + last interest payment
Real use: Bridge loans, developer financing, corporate bonds. Not common for residential mortgages.
What data do you need to calculate?
| Data | Description | Example |
|---|---|---|
| Principal | Total amount borrowed | €150,000 |
| Annual Interest (APR or nominal) | Fixed or variable rate (we use fixed for simulation) | 3.5% |
| Term | Years of loan duration | 30 years |
| System | French, German or American | French |
| Start Date (optional) | To see real months in schedule | 01/2025 |
What the calculator returns
- Monthly payment (or first payment in German system)
- Total interest paid over the whole loan
- Total paid (principal + interest)
- Complete amortization schedule with columns:
- Period (month)
- Date
- Payment
- Principal repaid
- Interest
- Outstanding balance
You can download or copy the schedule for your calculations, compare bank offers or plan early repayments.
Early repayment: is it worth it?
If you receive an inheritance, a bonus or save money, you can repay principal early. Two options:
| Option | What changes | When it makes sense |
|---|---|---|
| Reduce payment | Same end date, lower payment | If you want to ease your monthly burden |
| Shorten term | Same payment, finish earlier | Save more interest (recommended if you can) |
Tip: Ask your bank about early repayment fees (in Spain, max 0.5% first 5 years and 0.25% after for variable mortgage; 2% / 1.5% for fixed).
Try the calculator now
Enter your details and get the payment, amortization schedule and total cost of your loan instantly. Free, no sign-up, 100% in your browser.
Calculate your loan payment and schedule and get your complete table instantly.