Calculator
Overpay the mortgage or invest? A calculator with the break-even return
The same amount, the same monthly outlay, two options: overpay the loan or invest. The calculator computes net worth at the end of the original loan term, after capital-gains tax, and gives one number – the investment return above which not overpaying pays off.
At the end of the loan term you have more from
overpaying
- overpaying175 827 zł
Overpay; after payoff the former instalment is invested
- investing155 443 zł
Same amount invested, loan per schedule
- Investing wins only from
- 6,7 %
- Interest saved by overpaying
- 105 953 zł
- Loan shorter by
- 4 yrs 9 mo.
- Overpaying gives a certain, tax-free return equal to the loan rate. Investing gives an expected return, not a guaranteed one.
- The 6,7 % break-even is before capital-gains tax; below it overpaying wins in every scenario.
- Emergency fund first (3–6 months of costs) – the bank will not give overpaid money back when you need it.
Indicative result – not a loan offer or investment advice. Statutory and market parameters checked on 2026-10-10.
An indicative tool: the result is an order of magnitude on your assumptions, not a valuation or tax, legal or investment advice. Data entered into the form is never sent or stored anywhere.
How the comparison works
- 1Option A: overpayThe amount goes to principal in “shorter term” mode. The instalment stays, but the loan ends earlier – from that month the former instalment is invested monthly until the end of the original term.
- 2Option B: investThe amount is invested at once and works for the whole term; the loan follows its schedule. In both options you spend the same every month – the comparison is fair.
- 3Break-evenI search for the return at which both options give the same after-tax net worth. It is the question from the other side: how much the investment must earn for the risk to be worth it.
Frequently asked questions
Is overpaying a mortgage a good investment?
It is an investment with a certain, tax-free return equal to the loan rate. At 6–8 % a safe alternative paying more after tax is hard to find. With an old fixed rate of 2–3 % – usually not.
Overpay or buy treasury bonds?
Inflation-linked bonds (EDO, COI) pay inflation plus a margin, minus 19 % tax. When the loan rate exceeds that net return, overpaying wins. Inside an IKE bond account, tax-free, it can be close to a draw.
What if I have no emergency fund?
Emergency fund first: 3–6 months of costs in an account or short-term bonds. Only then split the surplus between overpaying and investing. You cannot “withdraw” a loan in an emergency.
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