In short
With 400,000 zł left to repay over 25 years, overpaying 300 zł a month saves about 88,141 zł in interest, and a margin 0.5 pp lower about 36,274 zł. Together they save about 113,948 zł, less than the sum, because an overpayment saves less interest at a lower rate.
What each option saves
Example: 400,000 zł over 25 years at 6.01% (WIBOR 3M 3.89% plus a margin of 2.12%), equal instalments. An overpayment shortens the term, a lower margin lowers the instalment.
| Option | Instalment | Interest to the end | Less interest | Loan ends after |
|---|---|---|---|---|
| No change | 2,580 zł | 373,895 zł | - | 25 years |
| Overpayment 300 zł a month | 2,580 zł + 300 zł | 285,754 zł | 88,141 zł | 19 years 11 months |
| Overpayment 1,000 zł a month | 2,580 zł + 1,000 zł | 187,678 zł | 186,217 zł | 13 years 9 months |
| Margin 0.5 pp lower | 2,459 zł | 337,622 zł | 36,274 zł | 25 years |
| Margin 1 pp lower | 2,341 zł | 302,207 zł | 71,688 zł | 25 years |
| Margin 0.5 pp lower and 300 zł a month overpayment | 2,459 zł + 300 zł | 259,947 zł | 113,948 zł | 20 years |
WIBOR 3M unchanged until the end, margin: the average market margin plus 0.3 pp. No early repayment fees or refinancing costs.
Three ways to pay less
- A lower margin at your bank. Ask your bank to lower the margin to what it offers new clients today. It costs nothing, but the bank does not have to agree.
- Refinancing. Moving the mortgage to another bank with a lower margin. From the gain deduct the valuation, notary and land register fees and, in the first 3 years, the early repayment fee. See the refinancing calculator.
- Overpayment. Extra payments shorten the term or lower the instalment. With a variable rate the bank may charge a fee only in the first 36 months, at most 3% of the amount. See the overpayment calculator.
Frequently asked questions
How much do I save by overpaying 300 zł a month?
On 400,000 zł over 25 years at 6.01%: about 88,141 zł in interest, and the loan ends after 19 years 11 months instead of 25 years. Overpaying 1,000 zł a month saves about 186,217 zł.
How much does a margin 0.5 or 1 pp lower save?
In the same example a margin 0.5 pp lower cuts the instalment by 121 zł and interest by about 36,274 zł. A margin 1 pp lower cuts the instalment by 239 zł and interest by about 71,688 zł.
When does refinancing not pay off?
When the margin difference is small and only a few years are left: the costs of moving (valuation, notary, land register fees and, in the first 3 years, the early repayment fee) eat the gain. It also does not pay off when the new bank requires extra products, such as insurance, that cost more than the margin cut.
Sources
This guide describes general rules and typical bank practice as of October 2026. Details
It is not legal or tax advice and not a bank offer. Each bank sets its own criteria, and the lending decision is always made by the bank.
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