What is the Compound Interest?
Compound interest means each period’s interest is added to the principal, and the next period’s interest is calculated on that bigger amount. Money starts working on money. Einstein reputedly called it the eighth wonder of the world; your bank calls it "quarterly compounding" on the FD receipt.
The more frequently interest compounds, the more you earn: ₹1 lakh at 8% for 10 years becomes ₹2.159 lakh with yearly compounding, ₹2.208 lakh with quarterly and ₹2.22 lakh with monthly. Frequency matters — but time matters far more.
Formula & worked example
where P is the principal, r the annual rate, f the number of compounding periods per year and n the years.
Worked example: ₹1,00,000 at 8% for 10 years, quarterly compounding → A = 1,00,000 × (1 + 0.02)40 ≈ ₹2,20,804. Simple interest for the same terms would pay only ₹80,000; compounding adds ₹40,804 on top — for doing nothing but waiting.
How to use this compound interest calculator
- Enter the principal, annual rate and years.
- Choose the compounding frequency from the product’s terms — FDs: quarterly; most bonds: half-yearly; savings accounts: daily balance, quarterly credit; loans: monthly.
- Compare the compound result with the simple-interest line to see the compounding bonus.
Smart tips
- Time beats rate: 8% for 30 years (10.1×) beats 12% for 15 years (5.5×). Start early, stay invested.
- When comparing products, always compare the effective annual yield, not the nominal rate — this calculator shows the true maturity.
- Compounding works against you on loans and credit cards at 36–42% APR — the same math that builds wealth destroys it.
- Reinvest payouts: choosing an FD/fund "cumulative/growth" option instead of payout keeps compounding intact.
- Small differences compound: 1% extra return on ₹10L over 20 years is worth ₹8.9 lakh more.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is paid only on the original principal every period. Compound interest is paid on principal plus all accumulated interest, so the balance grows exponentially instead of linearly. Over long periods the gap becomes enormous.
What does compounding frequency mean?
How often interest is calculated and added: yearly, half-yearly, quarterly, monthly or daily. Higher frequency at the same nominal rate gives a slightly higher effective yield — 8% compounded monthly is an effective 8.30% a year.
Which Indian products compound how often?
Bank FDs and RDs: quarterly. PPF: yearly. Savings accounts: interest computed on daily balance, credited quarterly. Most mutual funds compound continuously through NAV. Loan EMIs: monthly.
How can I benefit most from compounding?
Start early, add regularly, never interrupt. A 25-year-old investing ₹5,000/month at 12% has ~₹2.6 crore at 55; starting at 35 gives just ~₹95 lakh — a 10-year delay costs two-thirds of the outcome.
Does this work for crypto/stocks that have no "interest"?
Yes — use your expected annual growth rate as r with yearly compounding. The formula models any asset that grows at a compound rate, which is how CAGR is defined.
Want the theory behind the numbers? Read our money basics guides on the Money Blog.