How to use the component replacement reserve calculator
- List each component on its own line: name, cost today, whole years until replacement and the balance already set aside (optional).
- Enter the yearly cost inflation and the interest the fund earns.
- Read the future cost, the amount still needed and the yearly contribution for each component.
- Check the totals, then download the CSV to share the plan.
Formula
Future cost = cost today x (1 + inflation)^years
Balance at replacement = balance x (1 + interest)^years
Still needed = future cost - balance at replacement, at least 0
Yearly amount = still needed x interest / ((1 + interest)^years - 1)
Contributions are made at the end of each year. With 0% interest the yearly amount is still needed divided by the years, and a component due now shows the full amount.
Four building components
A roof costs $85,000 today, is due in 12 years and has $20,000 set aside. At 3% inflation it will cost $121,189.68, the $20,000 grows to $25,364.84 at 2%, and the $95,824.84 still needed means $7,144.66 a year.
Add paving ($6,521.89 a year), an elevator ($4,627.16) and painting ($5,733.46) and the four components need $24,027.17 a year, against $284,487.00 of future cost.
Why plan by component
Buildings wear out in pieces. A roof, a parking area and an elevator each have their own life and cost, so funding them one at a time shows what must be put aside every year to avoid a large special charge when one fails. A single sinking fund treats the goal as one lump, while a component plan shows which items drive the yearly amount.
Inflation matters as much as interest. A cost that rises 3% a year is 43% higher after 12 years, so a plan that ignores it falls short even if the balance earns interest.
Using the plan sensibly
Components with a short life dominate the yearly amount because there is little time for interest to help. Painting due in 3 years needs most of its cost within 3 payments, while a roof due in 12 years is spread out. When a component is replaced, restart its line with a new cost and life.
A formal reserve study by a qualified professional looks at the real condition of each item and local rules may set funding requirements. Use this page for planning and for checking a study, and update it each year.
Assumptions and limits
- Lives are whole years from 0 to 100, and each component is replaced once in the period shown.
- Inflation and interest are constant. Contributions are level and made at the end of each year.
- The page does not model taxes, fees or the order in which the components are due.
- The figures are examples. Nothing is uploaded.
Frequently asked questions
What if a component is already underfunded?
Enter the balance you have. The yearly amount rises to make up the shortfall over the remaining years.
What does a life of 0 mean?
The component is due now. The tool shows the full amount still needed after the balance, as one payment.
Should I use a high inflation rate?
Use a rate you can support from your own cost history or from local quotes, since the cost of building work can move differently from general prices.
Can the interest rate be negative?
Yes, down to -50%, if you want to test a loss. A rate of 0 is handled separately.