Interactive calculator
Compound Growth Calculator
Small growth rates compound into large changes: future value = present value x (1 + g)^t. Enter a starting value, an annual growth rate, and a horizon — for example, 2% growth over 35 years roughly doubles the starting value — and watch each year's value accumulate. In this release this page is powered by the closest available interactive widget; a dedicated widget for this topic is planned.
Spending Multiplier Calculator
k = 1 ÷ (1 − MPC), then ΔY = k × ΔG
Multiplier k = 5.000
Total GDP change ΔY = 500.00
Steps
- Marginal propensity to save: MPS = 1 − MPC = 1 − 0.80 = 0.20
- Multiplier: k = 1 ÷ MPS = 1 ÷ 0.20 = 5.000
- Total change: ΔY = k × ΔG = 5.000 × 100.00 = 500.00
- Round by round (each round respent at rate MPC): R1 = 100.00 → R2 = 80.00 → R3 = 64.00 → R4 = 51.20 → R5 = 40.96 → … converging to 500.00.
Why it works
The first round adds ΔG to GDP. A share MPC of that income is respent, adding MPC × ΔG, then MPC² × ΔG, and so on. This geometric series sums to ΔG × (1 + MPC + MPC² + …) = ΔG ÷ (1 − MPC).
How to use it
Enter the starting value.
Enter the annual growth rate.
Enter the number of years and read the projected value.
What you will learn
- Apply the compound growth formula.
- Explain why sustained small differences in growth matter.
- Connect compounding to long-run living standards.