There is no universal answer: paying down a mortgage can reduce future interest costs, while investment returns are uncertain and depend on risk, timescale and charges. Check whether your mortgage allows overpayments and whether any conditions or fees apply, then compare this with your investment options after tax and costs. It may also be sensible to keep an emergency fund and consider any available employer pension contribution before making extra mortgage payments. Your decision should reflect your circumstances and attitude to risk; check current rules with your lender, Revenue or a regulated financial adviser.