# Simple and Compound Interest important Formulae

1. Simple Interest, SI = PTR/100

2. Principal, P = 100 * SI/RT

3. Rate, R = 100 * SI/PT

4. Time, T = 100  SI/RP 5. Amount, A = P + SI = P + (PTR)/100

6. If a certain sum of money becomes n times itself at R% p.a. simple interest in T years, then T = [(n-1)/R] * 100 years

7. If a certain sum of money becomes n times itself in T years at a simple interest, then the time T’ in which it will become m times itself is given by T = (m-1/n-1)  T years 8. If a certain sum of money P lent out at SI amounts to A1 in T1 years and to A2 in T2 years, then P = (A1T2-A2T1)/(T2-T1), R = (A1 – A2)/(A1T2 – A2T1)  100%

8. Compound Interest, CI = ? 1 + ? 100 ? − ? = ? 1 + ? 100 ? − 1

9. Amount, A = ? 1 + ? 100 ? , if interest is payable annually

10. Amount, A = ? 1 + ? ′ 100 ? ′ , R’= R/2, n’ = 2n; if interest is payable half-yearly

11. Amount, A =? 1 + ? ′′ 100 ? ′′ , R’’= R/4, n’’ = 4n; if interest is payable quarterly

12. When time is fraction of a year, say 43 4 years, then Amount, A = ? 1 + ? 100 4 × 1 + 3 4 ? 100

13.When Rates are different for different years, say, R1, R2, R3 for 1st , 2nd & 3rd years respectively, then, Amount = ? 1 + ?1 100 1 + ?2 100 1 + ?3 100

14.In general, interest is considered to be Simple unless otherwise stated.