Compound Interest Calculator
Your numbers
Result
Albert Einstein famously called compound interest the eighth wonder of the world: "He who understands it, earns it; he who doesn't, pays it." Unlike simple interest, compound interest reinvests the interest earned back into the principal, so that in the next compounding period, you earn interest on both your initial capital and your accumulated interest.
The FinToolkit Compound Interest Calculator allows you to project growth across different compounding intervals—annually, half-yearly, quarterly, and monthly—showing you the exponential difference that compounding frequency and time horizon make.
The compound interest formula
The mathematical formula for compound interest with periodic compounding is:
Compound Interest (CI) = A − P
Where:
• A = Final maturity amount
• P = Initial principal invested (₹)
• r = Annual interest rate (as decimal, e.g. 8% = 0.08)
• n = Compounding frequency per year (1 for annual, 2 for half-yearly, 4 for quarterly, 12 for monthly)
• t = Number of years
Worked calculation example
Consider an investment of ₹1,00,000 at an interest rate of 8.00% per annum over a 5-year tenure with annual compounding (n = 1).
| Year | Opening Principal | Interest Earned (8%) | Closing Balance |
|---|---|---|---|
| Year 1 | ₹1,00,000 | ₹8,000 | ₹1,08,000 |
| Year 2 | ₹1,08,000 | ₹8,640 | ₹1,16,640 |
| Year 3 | ₹1,16,640 | ₹9,331 | ₹1,25,971 |
| Year 4 | ₹1,25,971 | ₹10,078 | ₹1,36,049 |
| Year 5 | ₹1,36,049 | ₹10,884 | ₹1,46,933 |
| 5-Year Total | ₹1,00,000 | ₹46,933 (Total Interest) | ₹1,46,933 |
In Year 1, interest is ₹8,000. By Year 5, annual interest grows to ₹10,884 purely because past interest was compounding. Total compound interest earned is ₹46,933, compared to ₹40,000 under simple interest.
Impact of compounding frequency
The more frequently interest is calculated and added to the principal, the faster the balance expands:
- Annual compounding (n=1): ₹1,00,000 at 8% for 5 years = ₹1,46,933 (Effective Yield: 8.00%)
- Half-yearly compounding (n=2): ₹1,00,000 at 8% for 5 years = ₹1,48,024 (Effective Yield: 8.16%)
- Quarterly compounding (n=4): ₹1,00,000 at 8% for 5 years = ₹1,48,595 (Effective Yield: 8.24%) — standard in Indian bank FDs.
- Monthly compounding (n=12): ₹1,00,000 at 8% for 5 years = ₹1,48,985 (Effective Yield: 8.30%)
Frequently asked questions
What is the difference between nominal rate and Annual Percentage Yield (APY)?
The nominal rate is the stated headline interest rate (e.g. 8%). The Annual Percentage Yield (effective rate) is the actual return earned when compounding frequency is accounted for. For an 8% nominal rate compounded quarterly, the effective annual yield is 8.24%.
How does compounding work against you in loans?
When you borrow via revolving credit cards or unpaid personal loans, interest compounds against you monthly. A 3.5% monthly credit card interest rate compounds to an effective annual rate of over 51% per year.
How can I maximize the benefit of compounding?
Start investing as early as possible and avoid withdrawing returns. The true power of compounding emerges in the second and third decades, where annual interest gains begin to dwarf original capital contributions.
Related investment tools
- SIP Calculator — see how regular monthly investments compound across mutual fund market cycles.
- Fixed Deposit Calculator — calculate bank FD proceeds with standard quarterly compounding.
- Rule of 72 Calculator — determine how quickly your money doubles under compound interest.
- CAGR Calculator — measure the geometric annual compounding rate of past portfolio growth.
Trust, accuracy and transparency
Educational purpose
FinToolkit is an educational tool. Nothing here is investment, tax, insurance or legal advice, and no result should be treated as an offer or a quote.
Financial accuracy
Every result is produced by a published formula running at full double precision in your browser. Only the displayed figures are rounded.
Formula verification
Each formula is checked against the standard method used by Indian lenders, fund houses, insurers or the relevant statute, and re-verified whenever rules change.
Data sources
Rules and rates are taken from official sources such as the Income Tax Department, RBI, SEBI, EPFO, PFRDA and India Post.
Privacy commitment
Calculations run entirely on your device. We do not store, transmit or sell the figures you enter. See our privacy policy.
Review policy
Pages carry a last-updated and next-review date. Corrections are welcome through the contact page.