Repair or replace: a practical decision formula for appliances, phones, and cars
2026-07-19
The familiar “repair if it costs less than half of new” rule leaves out the most important variable: how many reliable months the repair actually buys. A $250 repair can be poor if it buys six months and excellent if it buys three years.
Direct answer
Repair when its expected cost per reliable month is below the net replacement cost per useful month, unless safety, warranty, parts or downtime overrides the math. Do not rely on a universal repair-cost percentage. In this example, repair costs an expected $418 over 36 months, or $11.61/month; replacement costs $1,250 net over 96 months, or $13.02/month. Repair is lower by $1.41/month and the current quote must stay near or below the $301 break-even level.
Inputs to collect
- Written repair quote still avoidable
- Reliable months the repaired item is expected to add
- Low/base/high chance of the same or related failure recurring
- Future cost if that failure occurs
- Old item’s incremental monthly energy or operating cost versus replacement
- Replacement out-the-door price with delivery, setup, tax, transfer or data migration
- Real trade-in, salvage or resale offer for the current item
- Useful months expected from a like-for-like replacement
- Warranty, parts, recall, safety and downtime facts kept beside the calculation
Formula
Expected repair-path cost = quote + recurrence probability × recurrence cost + extra monthly energy × repaired-life months. Repair monthly equivalent = expected repair cost ÷ repaired-life months. Net replacement = purchase + required fees − current-item value. Replacement monthly equivalent = net replacement ÷ replacement-life months. Break-even quote = repaired-life months × replacement monthly equivalent − expected recurrence − energy penalty.
Worked example
A repair quote is $250 and is expected to add 36 months. A 20% recurrence chance on a $300 future repair adds $60; $3/month extra energy adds $108. Expected repair-path cost is $418, or $11.61/month. A $1,200 replacement plus $100 setup less $50 resale costs $1,250 over 96 months, or $13.02/month. Repair wins by $1.41/month; its quote break-even is about $301.
Sensitivity check
| Scenario | Changed input | Result |
|---|---|---|
| Low recurrence | 5% instead of 20% | Repair $10.36/month |
| Short repair life | 18 instead of 36 months | Repair $20.22/month; replacement wins |
| No energy penalty | $0 instead of $3/month | Repair $8.61/month |
| Higher repair quote | $350 | Repair $14.39/month; replacement wins |
Compare your written repair quote with replacement
Limitations
- Probability and remaining life are user scenarios, not model-specific failure statistics.
- Safety-critical failures, recalls, water/fire damage, unavailable parts or unreliable diagnosis can rule out repair regardless of monthly cost.
- A car needs financing, insurance, downtime, resale and the condition of other systems; a phone needs data, battery, security-update and trade-in terms.
- Already-paid nonrefundable diagnostic fees are sunk unless the choices treat them differently.
Sources and verification
- FTC — read warranty repair, replacement and service-contract terms
- European Commission — repair obligations, parts and indicative prices
- CPSC — check recalls before continued use or repair
Last verified:
Repair versus replacement life-extension calculator
Compare monthly equivalents over each option’s expected useful months. Use quote-based scenarios; no failure rate is assumed for you.
- Expected repair-path cost
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- Repair cost per useful month
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- Net replacement cost
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- Replacement cost per useful month
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- Quote / net replacement
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- Maximum break-even repair quote
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Educational estimate. Safety, warranty, diagnosis, downtime and financing can override the arithmetic.
Get a written diagnosis before assigning recurrence risk
Ask which component failed, whether the quote is capped, what labor and parts are warranted, and whether related wear was inspected. Use a low/base/high recurrence scenario instead of a web-wide average that does not match the model or failure.
Compare net replacement, not the sticker
Add delivery, setup, tax, data transfer or registration and subtract only a real trade-in or resale offer. Financing cost and downtime belong in additional scenarios. A car also needs remaining loan balance and resale treatment.
Energy difference is monthly and incremental
Use measured consumption and your current marginal rate. For a phone the difference may be negligible; for an old refrigerator, HVAC system or inefficient vehicle it can change the break-even quote.
Safety and warranty can override the result
Check recalls and the written warranty before authorizing work. Do not repair a safety-critical product based only on low monthly cost, and do not pay for a repair that the seller or manufacturer must cover.
General education only, not product-safety, vehicle, legal, tax or financial advice.