Multi-Year Projection Calculator
Project a value over many years at a growth rate — with an optional step change part-way through, the doubling time, and the year a target is reached.
Compounding is the whole story: at 7% a year a value doubles in about ten years and quadruples in twenty.
How the multi-year projection calculator works
Compounding is the whole story: at 7% a year a value doubles in about ten years and quadruples in twenty. The rule of 72 gives the doubling time as 72 divided by the rate.
The step change models a one-off event — a new site, a price rise, a lost contract — that shifts the level in one year while the growth rate carries on. Most real projections have at least one.
Formula: value(t) = start × (1 + g)^t × (1 + step if t ≥ step year)
Worked examples
| Inputs | Value at the end | Note |
|---|---|---|
| 7% for 15 years with a step in year 5 | 827,709.46 | about 827,000 |
| No step | 689,757.89 | pure compounding |
| A negative step | 482,830.52 | a lost contract in year 5 |
FAQFrequently asked questions
What is the rule of 72?
Doubling time is roughly 72 divided by the growth rate in percent. At 7% that is about ten years, and the exact figure here is 10.24.
What is a step change?
A one-off shift in the level — a new location, a price rise, a lost customer — that the growth rate then carries forward. It multiplies every later year.
Why is the effective rate higher than the growth rate?
Because the step is spread across the whole period as if it were growth. A 20% step over 15 years adds about 1.2 points to the annual rate.
Does growth really compound like this?
For fifteen years, rarely without interruption. Treat the projection as the arithmetic of an assumption, not a forecast of the world.
What if growth is negative?
It works — the value decays, and the doubling time becomes a halving time in spirit though the row shows a dash.
Where these figures come from
- Hubbard (2014) — How to Measure Anything — the case for ranges over point estimates
- Vose (2008) — Risk Analysis: A Quantitative Guide — Monte Carlo and the triangular distribution
- Saltelli et al. (2008) — Global Sensitivity Analysis: The Primer — one-at-a-time sensitivity and its limits
- HM Treasury — The Green Book — UK government appraisal guidance
Last checked: September 2026. The methods are textbook decision analysis: triangular distributions for three-point estimates, tornado ranking for sensitivity, and simple additive weighting for decision matrices.