The rough rule
If the repair costs more than about a third of a comparable new machine, and the machine is over four years old, replacement is usually better value. That's not a formula so much as a starting point — a three-year-old laptop with a cracked screen is worth fixing; a seven-year-old desktop that needs a drive and a power supply is not.
Repair is the right call when
Replace when
The cheap upgrade worth doing
If a machine is otherwise healthy but slow, and still has a mechanical hard drive, fitting an SSD is the single best value upgrade in computing. It routinely makes a five-year-old machine feel new for a fraction of replacement cost.
Budget for it instead of reacting to it
The most expensive way to buy computers is one at a time, urgently, because one died. A three or four year replacement cycle with one or two machines a year is cheaper, more predictable, and means nobody is working on the last surviving old laptop while they wait for a delivery.
We keep an asset list for plan clients with age and warranty status, so the conversation happens in a quarterly review rather than on a Tuesday morning when something has failed.