Mortgage overpayment or invest?

Short answer #

Mortgage overpayment provides a guaranteed saving equal to avoided mortgage interest where the contract allows it. Investing may earn more but remains uncertain and liquid. Compare after-tax return, risk and horizon.

Important variables #

• Mortgage rate and remaining term
• Allowed overpayment
• Expected return after cost and tax
• Emergency reserve and liquidity needs

Worked example #

A €10,000 overpayment at 4% avoids interest on an immediately lower balance. An investment expected to earn 5% has only a small uncertain lead before fees and tax.

Break-even: What changes the result? #

The higher the mortgage rate, the more attractive guaranteed repayment becomes. A longer horizon and greater risk capacity can make investing more relevant.

Common mistakes #

• Comparing gross return with mortgage rate
• Ignoring contract limits
• Using the entire reserve

Sources & assumptions

• European Central Bank — Bank interest rate statistics (2026-08-17)
• RATIOXA — Methodology and formulas (2026-08-17)