Save or pay off debt: why doing both at once is usually worse

You have $500 spare each month, a loan outstanding, and no savings. Where does the money go?

The answer depends on several things, but start here: splitting it between both is usually the worst available option. The debt shrinks slowly, the savings grow slowly, and neither task finishes within a foreseeable period. There’s a sense of movement and, for a long time, no result.

Here’s how to choose.

The simple comparison and its limits

The base logic is arithmetic. If the debt’s rate exceeds what your savings earn, every dollar does more work against the debt: you save more than you make.

Illustratively: a loan at 22% and a savings account at 4%. Those eighteen percentage points mean that $1,000 sent to the debt rather than the account leaves you meaningfully better off.

The reverse happens less often but does happen — a low fixed-rate mortgage while deposit rates are high. Early repayment then stops being obviously worthwhile.

The comparison has limits, and they matter. Rates move, agreements differ, some loans carry early-repayment fees, and savings may face withdrawal restrictions or tax on the interest. So the actual decision belongs with your own paperwork, and for substantial balances one conversation with a qualified adviser beats a calculation from a general article.

But first, a minimal buffer

Here practice overrides pure arithmetic, and most sources agree on it.

Send everything to the debt with zero reserve and the first surprise creates new debt. The fridge dies, treatment is needed, the car won’t start, and you borrow again — often at a higher rate than the one you were heroically paying down.

So the sensible order runs: a small buffer covering a typical surprise, usually one month of fixed costs. Then aggressive repayment of expensive debt. Then, and only then, growing the buffer further and pursuing other goals.

Sizing that first buffer is covered in the emergency fund. The point is that this target is modest and reachable within months, unlike “six months of expenses,” which with active debt takes years.

When behaviour beats arithmetic

Two repayment orders are well established: by rate, starting with the most expensive debt, and by balance, starting with the smallest.

The first saves more money. The second gets finished more often.

The reason is simple. A closed account produces a tangible result: one payment fewer, one worry fewer. That sustains momentum better than an interest calculation visible only in a spreadsheet.

If you have five debts and have already abandoned repayment twice, the smallest-first method may be better in practice despite being worse on paper. The difference in total interest is usually smaller than the difference between finishing and quitting.

With a single debt the question doesn’t arise.

Where the comparison doesn’t apply

Three situations where the general logic fails.

Debts already in arrears. This isn’t optimisation any more, it’s stopping penalties from compounding. The priority is obvious, and it’s often worth talking to the lender about restructuring rather than hunting for an optimal order.

Variable-rate debt. Comparing it against a fixed savings return is approximate at best, because one of the two numbers can move.

A credit card inside its grace period. If you clear the balance before interest applies, the rate formally never engages and the logic changes entirely.

With several debts

The first step is always the same: get everything onto one page. Balance, rate, term and minimum payment for each. For many people that table has never existed, and assembling it alone changes the picture.

Then one rule applies: minimums on everything, and all spare money into one chosen debt. Spreading the surplus evenly across all of them means closing none of them in any reasonable timeframe.

Which debt goes first follows the discussion above: the most expensive if you’re confident you’ll see it through, the smallest if you need visible progress.

When the first debt closes, its whole payment moves to the next one. That detail carries the method: if freed-up money dissolves back into the budget, the scheme stops working.

What happens to the freed-up payment

The point where this usually falls apart isn’t the beginning. It’s just after the first win.

The debt is cleared and the $400 monthly payment is no longer needed. Formally you now have $400 of free money, and it disappears within two months, because spending expands to fill what’s available automatically.

The only reliable defence: redirect the whole freed-up payment into the next target on the day the previous debt closes. Not next week, not after the holiday.

That’s harder than it sounds. You’ve spent six months economising, the debt is gone, and exhaling feels overdue. The compromise that usually holds: a small part of the freed amount goes to something enjoyable once, and the rest transfers onward automatically. Fitting it back into the plan is covered in saving when there’s nothing spare.

Review quarterly

Circumstances move, and so should the decision.

Deposit and loan rates change. Your income may rise. The debt shrinks, and at some point the remaining balance gets small enough that clearing it outright is psychologically simpler than continuing to optimise.

Once a quarter, look at three numbers: the outstanding balance, the size of the buffer, and the current rate. If the relationship has shifted, change the priority.

Fitting both the debt payment and the savings contribution into a plan is shown in the calculation from building a monthly budget: both enter before spending begins rather than being assembled from what’s left.

The order that suits most situations

Minimums on every debt, so nothing accrues penalties. A small buffer covering one month of fixed costs. Then everything spare into the most expensive debt until it’s gone. Then the next one. And only after the expensive debt is cleared, growing the buffer and pursuing longer-term goals.

That order isn’t mathematically optimal in every individual case, but it’s durable: people finish it more often than they finish elaborate schemes, and a plan carried to completion beats a perfect one that was abandoned.