Simple & compound interest

Simple interest

SI = P × R × T / 100

Amount (SI)

A = P + SI = P(1 + RT/100)

Compound amount

A = P(1 + R/100)ⁿ

Half-yearly: R/2 and 2n

CI − SI for 2 years

CI − SI = P(R/100)²

CI − SI for 3 years

CI − SI = P(R/100)²(3 + R/100)

Rule of 72

Years to double ≈ 72 / R

Approximate, for CI

CI, rate changes each year

A = P(1 + R₁/100)(1 + R₂/100)…

Equal instalments (SI)

x = 100A / [100T + RT(T − 1)/2]

x = each yearly instalment for debt A