Should I invest before paying off high-interest debt?

Generally no — if your debt carries an interest rate above 7–8%, paying it off first is the equivalent of a guaranteed, risk-free return at that rate. The stock market historically returns around 7–10% annually with significant short-term volatility. Paying off a 22% APR credit card balance is a guaranteed 22% return. Always capture your 401k employer match first (even while in debt), then prioritize high-interest debt repayment.