Pay Debt vs. Save Calculator

How it works

Paying down a balance is an investment in disguise. Every dollar you put toward it stops that dollar from being charged interest, so clearing a balance earns you a return equal to its interest rate, guaranteed and risk-free. The decision is a rate contest:

With the defaults, a 22% debt rate against a 7% expected return is a 15 point gap in favor of paying the debt. A guaranteed 22% is nearly impossible to beat in the market, and it comes with none of the risk. The logic flips only when your debt is cheap: a 3% or 4% loan is often worth keeping while you invest, because a diversified portfolio has historically returned more over long stretches.

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A worked example: $300 a month, 22% card

Picture a month where you finally have $300 of breathing room and one nagging credit card sitting at 22%. The question is whether that spare cash should chip at the balance or start growing in the market. The math says: pay the debt.

Clearing a balance that charges 22% is a locked-in 22% return, and it carries no risk at all. Investing that same money might earn you 7% over time, but nothing about that is guaranteed. The gap between the two is 15 points, all of it in favor of the debt.

That spread is the whole argument.

So the $300 goes at the balance until it is gone, then you redirect it toward investing. Plug in your own rate and expected return to see where the line tips for you.

The order that usually wins

• Grab any 401(k) match first. A dollar-for-dollar match is an instant 100% return, so capture it before even high-rate debt.
• Keep a small starter fund. A modest cash buffer stops the next surprise from landing back on a high-rate card.
• Then let the rates decide. Attack debt that costs more than you can reliably earn, and invest once your remaining debt is cheaper than your expected return.

Why the rate contest is not the whole story

Comparing your debt rate to an expected return is the right starting point, but a clean rate gap hides a few things that should tilt a close call.

• Guaranteed beats expected. Paying down debt returns its rate for certain. A market return is only an average over long stretches, with losing years mixed in, so a tie on paper should usually go to the debt.
• Liquidity has value. Money sent to a balance is hard to get back, while money invested in a taxable account can be sold if you need it. If your cash cushion is thin, that flexibility is worth something.
• Taxes change the comparison. Returns in a taxable account are trimmed by tax, so compare your debt rate against an after-tax return. Debt payoff has no such drag, which quietly favors it.
• Peace of mind is real. Some people sleep better debt-free even when the math narrowly favors investing, and that is a legitimate reason to lean toward payoff.

You can split the difference

This is not an all-or-nothing choice. When your debt rate and expected return sit close together, or you simply want progress on both fronts, dividing the extra money is a perfectly sound plan.

• Do both on purpose. Sending part of your spare cash to the balance and part to investing keeps the debt shrinking while your savings start compounding, and it hedges the guess you are making about future returns.
• Weight it toward the higher rate. If the debt clearly costs more than you expect to earn, tilt the split toward payoff. If the debt is cheap, tilt toward investing.
• Revisit as things change. A variable-rate balance that climbs, or a raise that frees up cash, is a reason to re-run this comparison and shift the mix.

The strict rate contest tells you where a dollar works hardest, but a split respects the fact that you are usually chasing more than one goal at once.

A worked example with a close call

Say you have $300 a month to deploy and a student loan at 6%, while you expect roughly 7% from a diversified index fund. On the numbers, investing edges ahead by about a point, so the tool leans that way.

Yet plenty of people still send that $300 at the loan, and reasonably so. The 6% saving is locked in, while the 7% is a long-run hope that could be lower over any given decade. Once you knock the expected return down for taxes, the gap can vanish entirely.

Flip the debt rate up to a 22% card, though, and the call stops being close: no reliable investment beats a guaranteed 22%, so the extra money belongs on the balance without hesitation. The wider the rate gap, the more clearly the math decides for you, and the narrower it is, the more your own comfort with risk gets the final say. It also helps to remember what you are really buying with each choice.

Paying the loan buys certainty and a smaller balance you can never lose to a market dip. Investing buys growth you expect but cannot promise, plus money you could reach in a pinch. Neither is wrong when the rates are close, so pick the one whose downside you would rather live with, and revisit it whenever your debt rate or your income changes.