A mechanic hands you an estimate for a few thousand dollars and you're staring at your car wondering if it's even worth it. There's no single right answer, but there is a straightforward way to think it through.
A common rule of thumb: if a single repair costs more than about 50% of the car's current market value, it's worth seriously considering letting it go instead. It's not a hard cutoff — a lot depends on the rest of this list — but it's a fast first filter before you spend more time on the decision.
The car is otherwise in good shape, the repair is a known, contained cost, and the total stays well under the car's value — routine maintenance, brakes, a battery, and most electrical or cosmetic issues generally fall here.
The repair is a major structural, engine, or transmission job; the car has a history of repeated breakdowns; or the total repair cost approaches or exceeds what the car is worth running. In these cases, selling the car as-is and putting that money toward a different vehicle is often the better math — especially if free towing and same-day payment are on the table, which removes most of the hassle of getting rid of a car that doesn't run.
If your car needs major work but individual components are still good, a junk car buyer or salvage yard values the vehicle for its usable parts and scrap metal — not just as a runner. That's often a better return than a trade-in on a car a dealer doesn't want.