Paying off high-interest debt is usually the best 'investment' available: every dollar of a 20% APR balance you eliminate earns a guaranteed, tax-free, risk-free 20% return — better than any market promise. The payoff time depends on the monthly rate and payment size through the amortization formula, and there is one iron rule: your payment must exceed the monthly interest charge, or the balance grows forever no matter how faithfully you pay. On $8,000 at 19.99%, monthly interest alone is about $133; a $100 payment would let the debt grow while you 'pay' it. Minimum payments are designed to keep you in debt for decades; anything above the minimum attacks the principal directly.
Two strategies dominate, and both beat spreading extra payments evenly. The avalanche — pay minimums everywhere, throw every extra dollar at the highest rate first — minimizes total interest mathematically and is the cheapest path out. The snowball — attack the smallest balance first regardless of rate — wins psychologically by delivering quick victories that keep you motivated. Avalanche is cheaper; snowball has better adherence; studies suggest most people do better with the method they will actually stick to. Either way, once a balance is clear, redirect its old payment to the next debt rather than absorbing it into spending — that is how the payoff accelerates like a snowball rolling downhill. And stop the bleeding first: no payoff plan survives new charges on the same cards.