Number Repair vs Replace Calculator
Every aging car, furnace and roof eventually asks the same question. This prices the repair in the only unit that matters — dollars per added year of life — sets it against the same unit for a replacement, and shows the classic 50% rule as the guideline it is, not a law.
Replacement cost should be net: the new item's price minus what the old one fetches as a trade-in or sale. "Value the repair adds back" matters for cars — a $2,800 transmission in a car worth $12,000 rarely adds $2,800 of resale value; $1,000 is a realistic default. The extra-running-cost line captures the old furnace's wasted gas or the old fridge's electricity appetite, per year of its added life.
How it works
Repair cost per added year = (repair quote + extra running cost × added years) ÷ added years. Replacement cost per year = net replacement cost ÷ replacement life. The cheaper unit cost wins the math verdict. The value-uplift input is reported separately — a repair that restores resale value effectively costs less if you sell soon after, but the uplift is speculative until a sale happens, so it never flatters the per-year figure here. The 50% rule — replace when a repair exceeds half the item's current value — is shown alongside as a guideline: it ignores how much life the repair buys, which is exactly the number that decides real cases. A repair at 60% of value that adds five years can be a bargain; one at 30% that adds six months can be a trap.
Formula & worked example
Formula: Repair cost per added year = (repair quote + extra yearly running cost × added years) ÷ added years. Replacement cost per year = net replacement cost ÷ expected replacement life. The 50% rule compares the repair quote with half the item's current value — a guideline shown beside the math, not a substitute for it. Any resale value the repair adds back is reported separately, never netted into the per-year figure.
Worked example: Car example: $2,800 ÷ 3 years = $933 per added year vs $26,000 ÷ 10 = $2,600 per year for the replacement. The quote is 23.3% of the car's $12,000 value.
When to use this
- A transmission, compressor or roof section fails and the quote is big enough to hurt
- An appliance repairer is at the door and you need the decision framework now, not tonight
- You are deciding whether an aging car earns one more repair or gets replaced
- A home warranty company offers a repair and you want to know if cash-out-and-replace beats it
How to use it, step by step
- Pick a preset to load typical figures, or enter your item's numbers directly.
- Enter the repair quote in full — then consider running it again padded by 30%.
- Estimate the years the repair adds; use the warranty period if one is offered.
- Enter the net replacement cost (after trade-in) and its expected lifespan.
- Add any extra yearly running cost of keeping the old item (fuel, electricity, repeat callouts).
- Read both signals: cost per added year for the math, the 50% line for the smell test.
What the inputs mean
| Input | What it is | Typical values |
|---|---|---|
| Current value | What the item is worth today in working condition — anchors the 50% rule. | For cars, a realistic private-sale value |
| Repair quote | The full out-the-door quote, parts and labor — pad it if discovery damage is likely. | Get it in writing; verbal quotes drift |
| Value the repair adds back | How much of the quote returns as resale value if you sell soon. Reported, never netted. | Often $0 for appliances; real for cars |
| Years of life added | The repairer's honest estimate — the input the whole decision turns on. | Ask directly; a warranty period is a solid floor |
| Replacement cost (net) / life | Installed price of the replacement minus trade-in or sale of the old item, over its expected life. | Use the quote for the model you would actually buy |
Another worked example
A water heater: the unit's remaining value is about $1,200, the repair quote is $650 — 54.2% of value, past the 50% guideline — and the repair buys about 2 more years, so $325 per added year. A replacement installed for $2,100 with a 10-year life costs $210 per year. Both the rule and the math say replace. The car example in the formula card shows the opposite verdict — which is the point of running both checks instead of trusting either alone.
When the light comes on
Ownership math meets the check-engine light in the Auto Repair Hub: decode any of the 9,533 OBD-II codes free, read the guide for your exact code, and price the repair for your state before a shop quotes it.
Frequently asked questions
What does the default car example say?
The $2,800 repair on a $12,000 car is 23.3% of value — comfortably under the 50% guideline — and at 3 added years it costs $933 per added year against $2,600 per year for the replacement. Repair wins clearly. The verdict flips when added life shrinks: at 1 added year the same repair costs $2,800 a year and loses.
Where does the 50% rule come from, and should I trust it?
It is a long-standing consumer heuristic: once a single repair passes half the item's value, the item is usually near end-of-life and further repairs tend to follow. Use it as a smell test. The cost-per-added-year math is the better tool because it prices what the repair actually buys you — time.
When is replacing better even if the repair is cheaper per year?
When reliability is the product: a work vehicle that cannot be down, a furnace in a cold climate, anything where failure costs more than the item. Also when the replacement is dramatically cheaper to run — an old heat pump replaced by a modern one can repay a chunk of its cost in energy savings, which the extra-running-cost line models.
How do I estimate "years of life the repair adds"?
Ask the repairer directly — a good shop will tell you whether the fix is a 1-year patch or a 5-year solution, and what else is likely to fail soon. For appliances, compare against typical lifespans: fridge 13 years, washer 10, water heater 8–12, roof 20–30 depending on material.
Should I count the money I have already spent on repairs?
No — that money is gone either way (the sunk-cost trap). Only future costs decide a future choice: the next repair quote, the remaining life each path buys, and the running costs ahead. Past repairs matter only as information about the item's condition.
🏠 Deciding on the house itself?
For big-ticket home systems, price the replacement properly first — roof, water heater and HVAC cost estimators use current planning ranges.
What if the repair comes with a warranty?
A warranty converts an uncertain added life into a guaranteed minimum — use the warranty period as your added-years floor and the repairer's estimate as the ceiling, then run the calculator at both ends. If repair wins even at the floor, it is a safe call.
How should I handle a repair quote that keeps growing?
Pad it. Discovery damage — the rot behind the wall, the second failing component — is the norm on older items. Run the decision at the quote and at quote + 30%; if the verdict flips between the two, get a firmer quote or lean replace.