Clear a 3.9 percent mortgage or keep building the taxable bridge before 55 Withdrawal

The way I framed it was: the mortgage isn't competing with the market, it's competing with the size of the hole I have to bridge. Clearing it cuts your required annual spend for the gap years, which shrinks the bridge on both sides. I paid mine off at a similar rate and the expected value was slightly worse, but my bridge went from seven lean years to seven comfortable ones, which changed whether I could stop at all. This is what I did, not advice, and a planner would probably tell you the spreadsheet is right.

I'd keep the 3.9% and invest, but with one condition: you have to actually invest it, every month, without touching it. Most people who make the mathematical argument end up with a mortgage and a slightly bigger car. If you know you'll keep the discipline for two years, the numbers are on your side. If you don't, the mortgage is a forced savings plan with a decent return.

Split it. I put half the surplus at the mortgage and half in taxable for three years, which felt like a fudge at the time and turned out fine. You don't get the maximum of either outcome and you don't get the worst version of either regret.

One factual thing to check before you decide: how your country's rules treat early withdrawals and whether there are any exceptions that would let you touch retirement money before 59 without a penalty. In some systems the bridge is smaller than people assume and the whole question changes. Worth an hour with someone who knows the rules where you live.