Under compound interest, interest is added to the principal at the end of each period and earns interest in later periods.
1Amount
Annually: A = P(1 + R/100)ⁿ
Half-yearly: A = P(1 + R/200)²ⁿ
Quarterly: A = P(1 + R/400)⁴ⁿ
Different rates each year: A = P(1 + R₁/100)(1 + R₂/100)(1 + R₃/100)
CI = A − P
2CI vs SI
For 2 years: CI − SI = P(R/100)²
For 3 years: CI − SI = P(R/100)²(3 + R/100)
3Multiplying sums
If a sum becomes k times in n years, it becomes kᵐ times in m × n years