Construction & estimating · Cost & planning
Cash-flow S-curve calculator
Monthly spend and cumulative S-curve from a total budget and profile shape, with peak month.
Standard: Beta-distribution spend profile · cumulative S-curve
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Inputs in the worked example
The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.
| Input | Value | Unit |
|---|---|---|
| Total contract value | 4800000 | $ |
| Duration | 14 | months |
| Shape a (early) | 2 | |
| Shape b (late) | 2.4 | |
| Retention | 5 | % |
Worked example — results
| Result | Value | Unit |
|---|---|---|
| Peak month | 6 | |
| Peak spend | $545,454 | |
| Spend at 50 % of time | 58 | % |
| Retention held at completion | $240,000 | |
| Month 1 | $94,765 | cum. 2 % |
| Month 2 | $255,255 | cum. 7 % |
| Month 3 | $378,552 | cum. 15 % |
| Month 4 | $466,597 | cum. 25 % |
| Month 5 | $521,476 | cum. 36 % |
| Month 6 | $545,454 | cum. 47 % |
| Month 7 | $541,014 | cum. 58 % |
| Month 8 | $510,915 | cum. 69 % |
| Month 9 | $458,285 | cum. 79 % |
| Month 10 | $386,750 | cum. 87 % |
| Month 11 | $300,672 | cum. 93 % |
| Month 12 | $205,600 | cum. 97 % |
| Month 13 | $109,307 | cum. 99 % |
| Month 14 | $25,357 | cum. 100 % |
Method, formulas and assumptions
- Monthly weight ∝ t^(a−1)(1 − t)^(b−1) at month mid-points, normalised to the total
- a = b gives a symmetric curve; b > a front-loads spend
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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.