€300,000 mortgage at 4%: monthly cost and total interest
Borrow €300,000 at 4% over 30 years and the standard repayment is €1,432.25 a month. Keep paying that every month for the full term and you’ll hand over €515,609 in total, of which €215,609 is interest and €300,000 is the amount you actually borrowed.
The scenario
€300,000 borrowed, a 4% interest rate held constant for the full term, repaid over 30 years on a standard annuity basis — the same repayment amount every month, split differently between interest and principal as the loan goes on. This is how repayments work for the vast majority of residential mortgages: level payments, shifting composition.
Year one, dissected
In the first year you pay €17,187 in total. Of that, €11,904 is interest and only €5,283 reduces what you owe — 69% of every euro you pay in year one goes to the bank as interest, not toward the debt itself. Your balance falls from €300,000 to €294,717 by the end of the year.
That looks discouraging if you’re expecting the balance to drop in a straight line. It won’t, and this isn’t a trick or a sign you’ve been sold a bad deal — it’s simply how amortisation works. Interest is charged on whatever you currently owe, and in year one you owe close to the full €300,000, so the interest charge is close to its maximum for the whole term. Principal repayment is the leftover: whatever the fixed monthly payment doesn’t consume in interest.
The long middle
The balance doesn’t fall evenly across the 30 years — it accelerates. After ten years, with a third of the term gone, you’d still owe €236,352 — the balance has fallen by less than a quarter. After twenty years, two-thirds of the way through, you owe €141,463, meaning the second decade cleared close to half as much debt again as the first.
The mechanism is simple once you’ve seen it once: as the balance falls, the interest charged on it falls too, so a larger share of each fixed monthly payment is freed up to repay principal. Early payments are mostly interest; late payments are mostly principal. Nothing changes about your monthly bill — €1,432.25 throughout — only what that payment is doing for you underneath.
What a different rate does
The rate is the single biggest lever on both your monthly repayment and what the mortgage costs you overall. Here’s the same €300,000 over the same 30 years at different rates:
| Rate | Monthly repayment | Total interest over 30 years |
|---|---|---|
| 3% | €1,264.81 | €155,332 |
| 3.5% | €1,347.13 | €184,968 |
| 4% | €1,432.25 | €215,609 |
| 4.5% | €1,520.06 | €247,220 |
| 5% | €1,610.46 | €279,767 |
| 6% | €1,798.65 | €347,515 |
A rate rise from 4% to 5% adds €178.21 to the monthly repayment, which sounds modest — but over 30 years it lifts lifetime interest from €215,609 to €279,767. Small differences in the rate compound over 30 years into large differences in total cost, which is exactly what amortisation predicts once you understand how the balance and the interest charge feed each other.
Try your own numbers
If your own mortgage amount, rate or term differs from this example, the mortgage calculator will work out your monthly repayment and total interest directly.
This example assumes a constant interest rate for the full 30 years, no fees or mortgage protection insurance, and no overpayments — all of which would change the real figures.