Investment & Returns
Compound Interest Calculator (Any Frequency)
Project your investment growth with any compounding schedule—monthly, quarterly, yearly, or even daily. Enter your initial investment, monthly contribution, years, interest rate, and variance to see base/low/high scenarios, a table, and downloadable results.
Author: Pawan (M.Tech Data Science, BITS Pilani). Reviewed by Internal QA & Data Validation.
Enter your details
Amount you invest on day 0.
Set negative to model monthly withdrawals.
Length of time you plan to invest.
Nominal annual rate.
Show low/high scenarios around the base rate.
The results are in
In 0 years, your projected corpus (base) is ₹0.
Low/high scenarios use the variance range you set.
Total invested
₹0
Future value (base)
₹0
Future value (low)
₹0
Future value (high)
₹0
| Year | Future value (Low) | Future value (Base) | Future value (High) |
|---|
Step-by-step calculation
- Convert the nominal annual rate to periodic rate:
r_period = rate / (100 × m)wherem= compounding periods per year. - Compute number of periods:
n = years × m. - Grow the principal:
FV_principal = P × (1 + r_period)^n. - Grow monthly contributions as an annuity:
FV_annuity = C × ((1 + r_period)^n − 1) / r_period. - Total future value =
FV_principal + FV_annuity. Repeat with (rate − variance) and (rate + variance) for low/high scenarios.
Excel / Google Sheets formulas
Use these cells and formulas to QA the calculator in Excel/Sheets. You can swap the FV() function for the manual power/annuity versions if you prefer to avoid built-ins.
Input layout (sample values)
| Cell | Label | Value |
|---|---|---|
| B2 | Principal (P) | 100000 |
| B3 | Monthly contribution (C) | 5000 |
| B4 | Years | 10 |
| B5 | Rate % (nominal p.a.) | 10 |
| B6 | Variance % (±) | 2 |
| B7 | m = compounding periods/year | 12 |
Core calculations (put in D column)
If FV() is unavailable, use =B2*(1+D2)^D3 + B3*(( (1+D2)^D3 -1)/D2) for the base future value.
Checks & helpful metrics
- QA: D4 should equal D10 + annuity FV; D7 should be far below D4 when the horizon is long and rate > 0.
- QA: D5 < D4 < D6; EAR should exceed the nominal rate when m > 1.
Theory: why compounding works (500 words)
Compound interest captures the effect of reinvesting earnings so that each period’s interest becomes part of the base for the next period. In mathematical terms, the classic future value formula A = P(1 + i)^n treats growth as repeated multiplication by (1 + i) across n periods. When you add regular contributions, the problem becomes an annuity. Each contribution starts compounding from the moment it is made, so the future value of the stream is the sum of individually compounded deposits. Financial calculators simplify this by using the annuity immediate formula FV = C × ((1 + i)^n − 1) / i, where i is the periodic rate and C is the periodic payment. Changing the compounding frequency adjusts the periodic rate and the number of periods: a nominal 8% with monthly compounding is 0.08 / 12 per month for 12 × years periods. Daily compounding pushes the rate per period even lower but increases periods, nudging the effective annual rate upward.
Variance scenarios matter because returns are rarely fixed. By letting users test rate ± variance, the calculator gives a range of plausible outcomes rather than a single point estimate. This mirrors sensitivity analysis used in financial planning. Total invested is a linear calculation—initial principal plus monthly contributions over the time horizon—while future value is exponential due to compounding. This divergence explains why long-term horizons and higher frequencies have outsized effects.
From an implementation standpoint, the calculator converts user inputs to periodic equivalents, computes projections for each year to feed both the chart and the table, and formats results in Indian numbering for readability. Edge cases: if rate or variance drives the periodic rate to zero, the annuity formula can divide by zero, so the code guards against that by short-circuiting to linear growth. Negative contributions are supported to model systematic withdrawals, which flip the annuity sign.
The Plotly chart renders three traces (base, low, high) across the year labels; the table mirrors the same data for precise reading. Sharing uses the Web Share API when available, with WhatsApp deep links as a fallback. PDF export relies on html2canvas plus jsPDF to snapshot the result card. All calculations run client-side; no user data is stored or transmitted. Rounding is limited to two decimals for display while internal math keeps full precision. This combination of mathematical rigor and UX touches (variance bands, chart + table, export/share) makes the tool a practical planning aid for SIP-style investing as well as one-time lumpsum growth.
References & credibility
- U.S. SEC Investor.gov — Compound Interest Calculator
- Investopedia — Compound Interest definition & formulas
- Reserve Bank of India — Saving and Power of Compounding (financial literacy FAQ)
- Corporate Finance Institute — Time Value of Money & annuity math
- NISM (India) Mutual Fund Workbook — SIP/compounding examples
Calcs are educational; verify rates and assumptions with your financial advisor.