A lot of boards already track the reserve fund in a spreadsheet: one column for the year, one for the balance, a formula that adds the contribution and interest and subtracts whatever got spent. That tells you how much money is in the account. It does not tell you whether that amount matches what the roof, the elevator, and the repaving job due over the next few years actually require.
A running-balance spreadsheet is easy to build and keeps the board honest about cash in and cash out. What it usually skips is a per-component model: each component's own remaining life, its own replacement cycle, and its own cost inflating independently until the year it is replaced and its cycle resets. Extending that correctly by hand, for six or eight components over a 30-year horizon, is a lot of interlocking formulas to get right and keep right as inputs change.
This calculator schedules every component on its own cycle, applies both special-assessment triggers boards actually use — a negative balance, and falling under a target percent-funded threshold — and solves for the minimum contribution that avoids the first shortfall, reporting it as a level annual figure, a one-time per-unit assessment, and a phased monthly per-unit increase.
| Question | Where to answer it |
|---|---|
| How much cash do we have right now? | Either one — a running balance answers this fine. |
| Does that balance match what today's component wear actually obligates? | This calculator's percent-funded figure, prorated per component rather than balance-over-total-cost. |
| What year does the fund fall short, given the real replacement schedule? | This calculator — each component modeled on its own life and reset cycle, not one aggregate line. |
| What contribution avoids that shortfall? | This calculator's solved minimum, instead of a manual guess-and-rerun loop. |
| Is anything I enter uploaded anywhere? | No. The calculator runs entirely in your browser; nothing is sent to a server. |
Usually one running balance: last year's number, plus this year's contribution and interest, minus whatever got spent. That answers "how much do we have" but not "is that enough", because it has no model of which components are due for replacement in which year or how their costs inflate between now and then.
Each component has its own remaining life, its own full replacement cycle, and its own cost that inflates independently until the year it is replaced — and then resets to a fresh cycle. A roof due in 8 years and a repaving due in 4 years are not the same formula extended by a different number of rows; get the reset wrong for even one component and every later year's percent-funded figure is off, silently.
Percent funded is a prorated, wear-based obligation — what the fund should hold today given each component's age relative to its life — not the fund balance divided by the sum of replacement costs. A sheet that divides balance by total future cost reads as far healthier than the fund actually is, because it never asks whether the money on hand matches what today's wear has already obligated.
Only by guessing a number, rerunning the whole schedule, and repeating until the shortfall year disappears — a manual binary search most boards do not have the formula patience for. This calculator runs that search the moment you enter your numbers and reports both the level annual contribution and the equivalent one-time special assessment and phased monthly increase per unit.
No, and neither is a spreadsheet. Both are planning estimates from assumptions you supply. A reserve study such as Florida's SB 4-D / SIRS requires a site inspection and a credentialed preparer; this tool and any spreadsheet are useful for interim planning between studies, or for sanity-checking one, not for satisfying the mandate itself.