Revival fails quietly: not one foolish purchase, but five reasonable ones that together cost a replacement. A ceiling, decided before you shop, is what keeps a good revival from becoming an expensive hobby.
Every other guide in this series tells you how to spend on an old PC. This one tells you when to stop. The 40 percent rule is a sanity line, offered openly as a rule of thumb: as revival costs approach roughly 40% of a suitable replacement's price, the burden of proof shifts to the repair. Below: how to price the replacement fairly, the traps that sneak people past the line, the honest exceptions, and a worksheet that turns an emotional decision into three numbers.
The verdict writes itself: this revival costs a sixth of the replacement and buys years. When your own worksheet's total creeps toward the 40% line, the comparison — not the repair — is what deserves your afternoon.
Here is the whole rule: when the total cost of reviving an old PC approaches roughly 40% of the price of a suitable replacement, stop and compare properly before spending more.
Two honest qualifiers. First, it is a rule of thumb from workshop experience, not a law of physics — your situation can justify crossing it (the next cards name the cases). Second, it compares against a suitable replacement — the machine that does the owner's actual job, not the cheapest box in the shop and not a dream build. Most revival mistakes are not bad repairs; they are good repairs bought one after another past the point where the money belonged elsewhere.
The revival order exists precisely to protect the budget: the free fixes (cleaning, startup discipline) cost nothing, the SSD costs a little and usually settles the question, RAM costs a little more and is bought only on a measurement. A plan that follows the order rarely reaches the 40% line, because it stops the moment the machine is fast enough.
The expensive pattern is the reverse: parts bought in hope order — a graphics card for a disk problem, RAM for a heat problem — each sensible alone, together a replacement's price spent on a still-slow PC.
Rules of thumb bow to facts. Spend past the line, eyes open, when: the machine does one light job perfectly well after a cheap fix; the needed part is already on your shelf; it is a learning machine whose whole value is being expendable; or the replacement genuinely cannot run something the old machine runs (an old peripheral, a licensed program tied to it). Sentimental value counts too — a family PC with a decade of history may be worth its repair. What the rule forbids is drifting past the line without noticing.
Total far under the line and years plural: revive. Total near the line and years singular: replace, and let the old machine become the hand-me-down or the Linux box. The worksheet takes ten minutes and has saved more money than any single repair in this series.
The video's revival is a model of spending in the right order — watch it, then run your own worksheet before buying anything.
▶️ Watch Full VideoNo — it is a rule of thumb, and this guide says so on purpose. It marks the point where you must stop and compare properly, not the point where spending becomes forbidden. A cheap SSD at any percentage is still a good buy; a third major part deserves the worksheet even if it sneaks in under the line.
Often the fairest one. Off-lease business machines are built to be serviced, and for browsing, documents and office work they outperform a revived consumer PC of the same money. Price one alongside the new basic machine before deciding — many revival verdicts flip at exactly this step.
Run the triage honestly — money spent does not change what the bottleneck is. Then apply the worksheet to the remaining spend only: the question is never what you have spent, it is whether the next step beats putting its cost toward a replacement. Sometimes one measured part finishes the job; sometimes the worksheet says stop, and stopping is the win.