Pay off debt or invest first?

In depth

Calculating the rate threshold honestly

At the next level, the simple “loan rate versus target return” comparison no longer holds — both sides must be measured after tax and risk. Paying down debt gives you the saved interest guaranteed and tax-free, whereas a stock return is uncertain and, in Germany, costs roughly 26.4 % capital-gains tax including the solidarity surcharge (as of 2026; exactly 26.375 % without church tax). Example: a loan at 4 % effective is like a guaranteed 4 % net “return”; to beat that with an ETF you need roughly 5.4 % expected gross return just to break even after tax. If you still have your annual saver’s allowance of 1,000 € (2,000 € for married couples) unused, that threshold shifts down a little. So the rule isn’t “rate below 5 % = invest” but “net cost of the loan versus net yield of the investment” — and when in doubt, the guaranteed side wins.

Ordering multiple debts

Once more than one loan is running, the order matters more than the basic question. The mathematically optimal method is the avalanche: pay the minimum everywhere and throw every extra euro at the most expensive loan — typically an overdraft at often 10–13 % or a credit card. Only once the expensive items are gone does the pay-down-or-invest question even arise for the cheap remainder. Watch out with mortgage overpayments: many contracts allow only a limited share of the remaining balance per year without an early-repayment penalty, and during the fixed-rate period an old loan at 1.5 % can almost never be sensibly repaid early. A common advanced mistake is eagerly paying down a 1.5 % mortgage while a 12 % overdraft quietly runs alongside. Always sort by interest rate, not by gut feeling or balance size.

Emergency fund before pure optimization

The biggest trap at this level is “winning” the math and then failing on liquidity. If you put every euro into debt or an ETF and keep no buffer, the next broken washing machine or car repair forces you back into expensive debt — instantly undoing the interest advantage. The sensible order is therefore: first expensive debt (overdraft, card), then an emergency fund of about three to six months of net spending, and only after that the finer pay-down-versus-invest call on the cheap loan. A widespread misconception is to see the emergency fund as “lazy” money; in fact it is the insurance that makes your whole strategy sustainable at all. If you’re self-employed, also plan reserves for tax back-payments and fluctuating income. Optimization only pays off once the ground beneath it holds.

The guaranteed vs. hoped-for gap

The reason high-rate debt usually wins is the certainty gap. Paying off a loan charging, say, an illustrative 12% is a guaranteed 12% return on that money: the interest you no longer owe is locked in the moment you repay. An investment that might average around 7% a year over the long run is an expectation, not a promise. It swings, it can fall for years, and the sequence of returns is out of your hands. So you are not really comparing 12% against 7%. You are comparing a certain 12% against an uncertain 7% that carries a real risk of being much lower over any given stretch. A rule of thumb that keeps beginners honest: when the loan rate clearly exceeds what a broad, diversified portfolio might reasonably return, treat repayment as the risk-free win and take it. When the loan is very cheap, close to or below that expected return, the certainty premium no longer justifies rushing, and running the loan alongside investing becomes defensible. The expensive mistake is treating a hopeful market average as if it were a bank statement. Discount uncertain returns before you compare; never discount the interest you are certainly paying, because that cost is the one number in the whole exercise you can fully trust.

Repayment is a one-way door

One thing beginners overlook is that repaying a loan and buying an investment are not equally reversible. Money you put into paying down a fixed-term loan is usually gone for good: except for a few flexible loans, you cannot pull it back out when an emergency hits. Money you invest, by contrast, can often be sold, though possibly at a loss if markets are down at that moment. This liquidity difference matters most for people whose accessible cash is still thin. Illustrative scenario: someone throws every spare euro at a low-rate loan, leaves almost nothing reachable, then faces a broken car and a gap in income in the same month. With no savings to draw on, they borrow again at a far higher rate and quietly undo the optimization they were so proud of. The framework here is to weigh not just which option earns more, but which keeps you out of forced, expensive borrowing later. A cheap, patient loan you could technically prepay is sometimes better left running while you keep cash reachable and investments liquid. Aggressive prepayment makes the most sense once your accessible reserves are solid, so that locking money away does not leave you one surprise from new debt.

The behavioral case for clearing debt

The spreadsheet is only half the decision; the other half is you. Even when the math narrowly favors investing over repaying a middling loan, debt carries a psychological cost that the numbers miss. An outstanding balance is a monthly obligation that shrinks your flexibility: lose income, and the payment still arrives on schedule. Many people also invest more calmly and consistently once debt is gone, because they are no longer mentally hedging every market dip against what they still owe. A concrete scenario: two savers with identical finances split on a borderline 5% loan. One keeps the loan and invests; a bad market year rattles them and they sell at the bottom, wrecking the theoretical edge they were chasing. The other clears the loan first, then invests steadily through the same dip and stays the course. The debt-free saver often ends up ahead, not because the arithmetic favored them, but because their behavior did. The takeaway is not to ignore the numbers, but to weight the calm of being debt-free when the gap is small. If carrying a loan would tempt you to panic-sell or quietly under-invest, the guaranteed return from clearing it is worth more than a fragile paper advantage that only survives on a good day.

Guard against the rate that changes

A loan rate is only a fixed target if the loan is actually fixed. Overdrafts, credit-card balances, and many lines of credit carry variable rates that can rise, and some cheap-looking loans start with a low teaser or promotional rate that later resets much higher. Comparing today's low rate against your expected investment return can flatter a debt that is about to become expensive. Before you decide a loan is cheap enough to run alongside investing, check three things: whether the rate is fixed or variable, when any promotional period ends, and how high the rate could realistically climb afterward. A common trap is a balance parked at a 0% promotional rate: it feels free, so it gets ignored, and then it flips to a steep ongoing rate on a date the borrower had long forgotten. The safer framework treats a variable or soon-to-reset debt as if it already carried its likely future rate, not its current one. If that future rate would clearly beat your expected return, prioritize clearing it now while it is still cheap, rather than being caught by the reset. Certainty cuts both ways: an uncertain loan rate deserves the same caution you would apply to any uncertain investment return.