Home Repair vs Replace Decision Calculator
Use the 50% Rule and Net Present Value analysis to decide whether repairing or replacing an appliance or home system makes more financial sense.
Formulas Used
1. 50% Rule
If Repair Cost ≤ 0.50 × Replacement Cost → lean toward Repair.
50% Threshold = 0.50 × Replacement Cost
2. Age Ratio
If Current Age / Expected Lifespan ≤ 0.75 → lean toward Repair.
Age Ratio = Current Age ÷ Expected Total Lifespan
3. Cost per Year of Service
Cost/Year (Repair) = Repair Cost ÷ Remaining Life After Repair
NPV of Savings = Annual Savings × [1 − (1+r)^−n] ÷ r
Net Replace Cost = Replacement Cost − NPV of Savings
Cost/Year (Replace) = Net Replace Cost ÷ New Lifespan
If Cost/Year (Repair) ≤ Cost/Year (Replace) → lean toward Repair.
4. Break-Even Year
Year at which cumulative discounted savings from replacement offset the extra upfront cost:
n = −ln(1 − ΔCost × r ÷ Annual Savings) ÷ ln(1+r)
where ΔCost = Replacement Cost − Repair Cost.
5. Weighted Decision Score
Score = (50% Rule signal × 40) + (Age Ratio signal × 20) + (Cost/Year signal × 40)
Score ≥ 50 → Repair; Score < 50 → Replace.
Assumptions & References
- 50% Rule: Industry rule of thumb — if repair cost exceeds 50% of replacement cost, replacement is generally preferred. (Consumer Reports, NAHB)
- 75% Age Threshold: Items beyond 75% of their expected lifespan are more prone to cascading failures; replacement is often more economical. (ASHRAE, Energy Star)
- Discount Rate: Represents the opportunity cost of capital or financing rate. Typical range: 3–8% for homeowners.
- NPV of Savings: Uses the present value of an ordinary annuity formula to discount future energy and maintenance savings.
- Typical Lifespans: HVAC 15–20 yrs, Water Heater 8–12 yrs, Refrigerator 10–15 yrs, Washer/Dryer 10–13 yrs (NAHB Study of Life Expectancy of Home Components, 2021).
- Annual savings estimates should come from manufacturer Energy Guide labels or utility audits.
- This calculator does not account for installation disruption, financing costs, or rebate/tax-credit incentives (e.g., IRA 25C credits).
- All costs are in nominal dollars; inflation is not modeled separately.