Compound Interest (Using Formula)

A = P(1 + r/100)ⁿ

A = P(1 + r/100)ⁿ, where A = Amount, P = Principal, r = Rate of interest per annum, n = Number of years. Compound Interest = A - P = P[(1 + r/100)ⁿ -

When rates differ for successive years

When rates differ for successive years: A = P(1 + r₁/100)(1 + r₂/100)(1 + r₃/100)... where r₁, r₂, r₃ are rates for consecutive years

A = P(1 + r/(2×100))^(n×2)

A = P(1 + r/(2×100))^(n×2). Rate is halved and time is doubled because interest is calculated twice per year

Using the basic formula to find

Using the basic formula to find unknown values: Principal when amount is known, rate when principal and amount are known, or time when other variables

For time like 2½ years

For time like 2½ years: A = P(1 + r/100)²(1 + r/(2×100))^(½×2). Complete years use annual compounding, fractional part uses half-yearly