Keep or Sell Car Calculator

Keep or Sell? The Financial Analysis

A car that keeps needing repairs feels expensive in a way a monthly finance payment does not, because repair bills arrive unpredictably and payments arrive on schedule. This calculator puts both on the same footing across a chosen period.

The comparison it makes is narrow and worth stating plainly. Keeping is priced as repairs alone: annual repair cost multiplied by the years. Replacing is priced as the finance on the difference between the replacement price and what the current car is worth as a trade-in, repaid over the same period, principal and interest together. At the defaults that is 6,000 against 14,599, so keeping wins by 8,599.

Two costs are missing, and both of them are missing in the same direction. The replacement car is charged at its full acquisition cost with no credit for what it is worth at the end of the period. The current car is charged nothing for the value it loses over those same years, even though it will be worth less at the end than the 8,000 entered at the start.

That makes the comparison structurally favourable to keeping, and by an amount that can be stated exactly. If the replacement is worth R at the end of the period and the current car loses L of its value across it, the true gap is 8,599 minus R minus L. Keeping stops being cheaper as soon as those two together exceed 8,599.

The one output that avoids the problem is the repair breakpoint. At the defaults it is 2,919.80 a year: the annual repair spend at which the two paths cost the same on the model's own terms. Against that, the 1,200 of expected repairs is 41% of the threshold, which is a more useful thing to know than the headline gap.

The Costs People Often Overlook

Depreciation drains money without ever sending an invoice, which is why it is the cost most often left out of a keep-or-replace decision. A newer vehicle loses value fastest in its early years, so replacing a well-depreciated car with something newer means absorbing a steep drop almost immediately. Accounting standards handle the same idea by spreading an asset's depreciable amount across its useful life and recognising a residual value at the end, and both halves of that matter here: the loss during the period, and what is left at the end of it.

Finance interest is the other quiet cost, and this model does include it. At the defaults, the 12,000 borrowed is repaid as 14,599, so 2,599 of the replacement cost is interest rather than car. Raising the rate does not change the price of the vehicle; it changes how much of the payment buys nothing.

What the Numbers Do Not Always Capture

A calculator works with figures, and several things it cannot weigh belong in the decision anyway. The reliability record of a specific vehicle is one, since expected annual repairs is an average and a car that has already had its expensive failures is not the same proposition as one that has not. Warranty cover on a replacement is another. So is the cost of being without a vehicle when one is off the road.

Where two options land close together, those factors reasonably decide it. Where they land far apart, as at the defaults, the gap is large enough that they are unlikely to.

A worked example

With a current car value of 8,000, expected annual repairs of 1,200, a replacement price of 20,000, a finance rate of 8% and five years to compare, the tool returns 8,599.00 in favour of keeping. The supporting rows show a keep cost of 6,000, a new car cost of 14,599, and a repair breakpoint of 2,919.80 a year.

The 14,599 is worth unpacking. The current car offsets the purchase as a trade-in, so the amount financed is 12,000 rather than 20,000, and repaying that at 8% over five years costs 2,599 in interest.

What moves the number most

Expected annual repairs is the input that decides the outcome, because it is the only thing on the keep side. It moves the gap by the number of years for every unit entered: at five years, adding 100 to annual repairs closes the gap by 500. Reaching the 2,919.80 breakpoint from 1,200 requires repairs to nearly two and a half times what is expected.

On the other side, the replacement price and the current value work as a pair, since only the difference between them is financed. Raising the replacement price by 1,000 has exactly the same effect as a trade-in worth 1,000 less. The finance rate matters least of the four at typical levels: it moves only the interest portion, which is 2,599 of the 14,599.

Years is the input that cuts both ways. It multiplies repairs on one side and spreads the loan on the other, so lengthening the comparison does not simply scale the answer.

The formula behind this

Keep cost is expected annual repairs multiplied by the number of years, and nothing else. Replacement cost is the amount financed, being the replacement price less the current car's value as a trade-in, repaid as a level monthly amortised payment at the given rate over the same period; the total of those payments is the replacement cost. The result is the difference between the two, labelled with whichever is lower, alongside the annual repair figure at which they would be equal.

Three things follow. The current car's value does not enter the keep side at all, only the buy side as a trade-in offset. No depreciation is calculated on either vehicle, despite depreciation being the largest cost of car ownership. And no residual value is credited to the replacement at the end of the period, so it is charged as though it were consumed entirely.

Where this calculation fits a purchase decision

The calculation itself is quick; the decision it informs usually is not. Separating the money side makes it easier to weigh cost against the things a single figure cannot carry, from the timing of a failure to how much a particular car is trusted.

Because the model is structurally favourable to keeping, a result that says keep by a small margin is weaker than it looks, and one that says buy is stronger than it looks: the buy side has to overcome an omission worth the replacement's residual value plus the current car's remaining depreciation before it wins at all.

What this doesn't capture

Running costs common to both paths are absent by design and largely cancel: insurance, fuel, tax and routine servicing continue either way, though a newer vehicle may shift each of them. One-off items do not cancel and are absent too, including transfer fees, taxes on purchase, and the cost of a failure that arrives outside the annual repair average. The International Energy Agency's analysis of cars and vans tracks how vehicle costs and fleet composition are shifting across regions.

The comparison also assumes the replacement is financed. Where it is bought outright, the interest disappears but the capital is still committed, and the opportunity cost of that capital is not modelled here either.