| Principal | Rate | Years | Deposit | Frequency | Illustrative Outcome |
|---|---|---|---|---|---|
| 10,000 | 8% | 10 | 200 | Monthly | Steady growth with deposits each month. |
| 25,000 | 6% | 15 | 0 | None | Pure compounding on a single lump sum. |
| 5,000 | 10% | 5 | 100 | Monthly | Higher rate increases interest share over time. |
| 50,000 | 4% | 20 | 500 | Yearly | Long horizons amplify compounding effects. |
| 12,000 | -2% | 3 | 0 | None | Stress-test outcomes under negative rates. |
- Compound growth (nominal): Future Value = P × (1 + r/n)^(n×t)
- Continuous growth: Future Value = P × e^(r×t)
- Simple growth: Future Value = P × (1 + r×t)
When deposits are enabled, the calculator builds a period-by-period schedule. Each period may include a deposit (beginning or end), then interest is applied, and optional tax is deducted from positive interest.
For display frequencies such as monthly or quarterly, the period rate is derived from the effective annual rate (EAR) so the schedule matches the annual rate assumption.
- Enter your starting principal, annual rate, and time horizon.
- Select an interest method and compounding frequency (if applicable).
- Add deposits, choose how often you contribute, and set timing.
- Optionally include taxes and inflation for more realistic estimates.
- Press “Calculate Growth” to see results above the form.
- Download your summary and schedule as CSV or PDF.
What the calculator measures
This tool projects how a balance grows from an opening principal, optional deposits, and a chosen annual rate. It reports future value, total contributions, gross interest, estimated tax, and net interest earned. For example, 10,000 starting value, 8% annual rate, 10 years, and 200 monthly deposits typically shifts the result so deposits drive a large share of ending value. CAGR is also shown, based on the opening principal, to summarize annualized performance and to help compare scenarios with different time horizons, contribution patterns, or compounding frequencies quickly.
Choosing an interest method
Compound mode assumes a nominal rate with n compounding periods each year, then converts it to an effective annual rate for consistent comparisons. Continuous mode uses exponential growth, while simple mode applies linear interest without compounding. The schedule display derives a period rate from the effective annual rate, so monthly, quarterly, and yearly tables remain aligned with the same annual assumption.
Impact of contributions
Deposits can be modeled monthly, quarterly, yearly, or per displayed period. Timing matters: contributions at the beginning of a period earn interest sooner than end of period deposits. If you contribute 200 monthly and switch timing to beginning, the first few periods show higher interest because the balance is larger before interest is applied. Longer horizons magnify this difference because compounding repeats on every period’s higher base.
Taxes and inflation adjustments
If you enter a tax rate, the calculator reduces positive interest each period and accumulates an estimated tax total. This creates a net growth path that is often closer to after‑tax reality for taxable accounts. Inflation adjustment discounts the future value by (1 + inflation)^years to estimate purchasing power. A 3% inflation assumption can materially lower a long‑term real value even when nominal returns look strong.
Reading the schedule output
The schedule table shows start balance, contribution, interest, tax, and ending balance for every period. Use it to locate when growth accelerates, test alternative rates, or plan deposit amounts to reach a target by a certain year. When a partial final period exists, it is prorated so time horizons like 7.5 years still produce consistent results.
How is future value calculated here?
The calculator builds a period schedule. It applies contributions (beginning or end), computes interest for the period rate, subtracts any tax on positive interest, then rolls the ending balance forward until the final period.
What is the difference between compound and continuous growth?
Compound growth uses (1 + r/n)^(n×t) with a selected compounding count. Continuous growth uses e^(r×t), which is slightly higher than frequent compounding at the same nominal rate.
Why do you show an effective annual rate?
Different compounding conventions can share the same nominal rate but deliver different outcomes. The effective annual rate converts the selected method into one comparable annual figure, used to derive monthly or quarterly period rates.
How do deposits affect the results?
Deposits increase the balance that earns interest. Earlier deposits usually grow more because they compound for longer. Changing frequency or timing can materially change the ending value, even when the annual rate stays constant.
How are taxes and inflation handled?
Tax is applied to positive interest each period at your entered tax rate, reducing net growth. Inflation adjustment discounts the final value by (1 + inflation)^years to estimate purchasing power in today’s terms.
Why might my manual formula differ from the schedule?
Timing and rounding matter. Deposits can occur at the beginning or end of a period, taxes reduce interest each step, and the display rate is derived from the effective annual rate to match your chosen schedule frequency.