ToolPetal
Compound interest calculator
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- Free, no sign-up
| Step | Value |
|---|
Growth sketch (equal steps, illustrative heights)
Not tax or investment advice. Ignores fees, taxes, and inflation. Contribution cadence matches compounding frequency.
Contribution cadence vs compounding cadence
On this page, contributions are locked to the same frequency as compounding. Frequency presets: yearly (1), half-yearly (2), quarterly (4), monthly (12, default), daily (365). If frequency is monthly, a contribution of Rs 5,000 means Rs 5,000 every month; if frequency is yearly, the same box means Rs 5,000 once a year.
Let P principal, r annual rate as decimal, n compounds/year, t years, C contribution per period:
FV = P×(1+r/n)^(n×t) + C×[((1+r/n)^(n×t) − 1) / (r/n)] when r/n ≠ 0. If the period rate is ~0, contributions become C × n × t. Deposits are end-of-period. This is textbook compound interest, not the India mutual-fund SIP end-of-month variant (use the SIP calculator for that).
No-contribution vs with-contribution (worked case)
Shared assumptions: P = Rs 1,00,000, rate 8%, monthly compounding, 10 years (120 periods).
| Case | C per month | Future value | Total contributions | Interest earned |
|---|---|---|---|---|
| Lump sum only | 0 | ≈ Rs 2,21,964.02 | Rs 1,00,000 (principal) | ≈ Rs 1,21,964.02 |
| Lump sum + deposits | 5,000 | ≈ Rs 11,36,694.20 | Rs 1,00,000 + Rs 6,00,000 | ≈ Rs 4,36,694.20 |
The second row is not a mutual-fund SIP formula; it is principal growth plus an ordinary annuity at the same monthly rate. For dated irregular flows, prefer the XIRR calculator.
Sanity checks before you trust a long horizon
Yearly compounding, C = 0, t = 1, rate 8% → FV should be P × 1.08. Rate 0 with contributions → FV = P + all contributions. More frequent compounding raises effective yield slightly when C = 0; when C > 0, remember you are also depositing more often if you leave C unchanged. Ignores taxes, fees, inflation, variable rates. Not investment advice. Disclaimer.
FAQ
What does this compound interest calculator compute?
It computes the future value of a starting principal grown at a stated annual rate with a chosen compounding frequency, plus optional regular contributions made at the same cadence as compounding. It also shows total contributions and interest earned.
What formula does the compound interest calculator use?
Let P be principal, r the annual rate as a decimal, n the compounds per year, t years, and C the contribution each compounding period (0 if none). Future value FV = P×(1+r/n)^(n×t) + C×[((1+r/n)^(n×t) − 1) / (r/n)] when r/n ≠ 0. When the periodic rate is 0, FV = P + C×n×t. Contributions are treated as end-of-period deposits.
Is this financial advice?
No. This is a browser-only math estimate. It ignores taxes, fees, inflation, and variable rates. It is not investment, tax, or lending advice.
Are my numbers uploaded?
No. Principal, rate, frequency, years, contributions, and the math run in your browser. Nothing is sent to ToolPetal.