Overpay or invest

Should spare money go into the mortgage or into the market?

Overpaying earns the mortgage rate, guaranteed and untaxed. Investing earns whatever the market gives, and the gain is taxed. This works out the return that would make the two come out level.As of 6 September 2026 · Reader-selected contract and tax assumptions

Your mortgage, and the spare money

Both paths spend the same amount every month. Only the destination changes.

Outstanding loan€ Mortgage interest rate%This is the return overpaying earns you, guaranteed and untaxed. Spare money each month€The amount whose destination is the question. Expected investment return% Compare overYears

Your loan contract

Original loan amount€The yearly overpayment cap is usually based on this amount, not today's balance. Contractual monthly payment€Use the instalment in the signed contract; it cannot be reconstructed reliably from today's balance and remaining years. Years left at the current fixed rateyears Years left on the loan Refinancing rate after that%Optional when the comparison ends inside the fixed-rate period; otherwise required as an explicit scenario. Yearly overpayment limit%Most German fixed-rate loans cap this at a share of the original amount. Zero means no cap. Anything refused is invested instead.

Tax on the invested money

Base tax rate on investment income% Fund partial exemption%Thirty percent is the default for a qualifying equity fund; zero is appropriate for individual securities and bank interest. Tax-free allowance each year€

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What this answers

Which destination leaves you better off

The same money goes in either way, for the same years. The difference between the two is the interest avoided against the growth earned, after tax.

What it does not answer

How certain either side is

The mortgage rate is contractual and the market return is a guess. A break-even the market has usually beaten is not a promise that it will, and paying down debt has a value no calculator can price.

Use the result

Compare it with what you would actually do

A guaranteed rate is worth more to somebody who would lose sleep over a bad decade. If the two are close, the tie-breaker is not arithmetic.