| Metric | Value | Copy |
|---|---|---|
| {{ r.label }} | {{ r.display }} |
| Year | Deposit ($) | Interest ($) | Ending ($) | Copy |
|---|---|---|---|---|
| {{ r.year }} | {{ money(r.depositCum) }} | {{ money(r.interestCum) }} | {{ money(r.ending) }} |
| Month | Deposit ($) | Interest ($) | Fees ($) | Ending ($) | Copy |
|---|---|---|---|---|---|
| {{ r.period }} | {{ money(r.deposit) }} | {{ money(r.interest) }} | {{ money(r.fee ?? 0) }} | {{ money(r.ending) }} |
Compound interest grows a balance by reinvesting returns on a schedule such as monthly or annually. Regular contributions add to the base and increase the effect. A clear schedule helps you see the balance, the share from contributions, and the share from interest over time.
Enter a starting amount, any recurring yearly or monthly contribution, a nominal annual rate, a compounding frequency, and a term in years and months. You can apply taxes to interest and a fixed or percentage fee and then compare the ending balance with and without inflation.
Payments made at the beginning of a period compound longer than those made at the end. Small fee rates can have a large effect over long horizons. Use the sensitivity view to see how close rates change the outcome around your default assumption.
This is a planning model. Markets change and actual returns vary from the assumptions used here.
Let P be the initial principal, c the combined monthly contribution from yearly and monthly entries, r the nominal annual rate, and m the number of months per compounding period. Interest credits after each period net of tax. Fees apply monthly as a percent of balance and a fixed amount.
| Symbol | Meaning | Unit/Datatype | Source |
|---|---|---|---|
| Initial principal | $ | Input | |
| Monthly contribution | $ | Input | |
| Nominal annual rate | % / yr | Input | |
| Months per period | 1, 3, 6, 12 | Input | |
| Rate per period | unitless | Derived |
Start 20,000, contribute 200 per month, rate 5, compounding monthly, term 5 years, no tax or fees.
Ending balance is the result of monthly deposits and monthly credits. Switching to end‑of‑period deposits lowers the ending value by a small margin.
| Field | Type | Accepted values | Notes | Placeholder |
|---|---|---|---|---|
| Initial | number | ≥ 0 | Starting balance | 20000 |
| Annual, monthly contributions | number | ≥ 0 | Combined into monthly | 0, 0 |
| Rate | number | ≥ 0 | Nominal annual percent | 5 |
| Compounding | enum | annually, semiann, quarterly, monthly | Maps to months | monthly |
| Term | integer | months ≥ 0 | Years plus months | 5 yr, 0 mo |
| Tax, inflation | number | ≥ 0 | Percent per year | 0 |
| Fees | number | ≥ 0 | Annual %, monthly fixed | 0, 0 |
| Input | Accepted Families | Output | Encoding/Precision |
|---|---|---|---|
| Principal, contributions, rate, term | Numbers and enums | Ending balance, interest, fees | 2 decimals for money |
| — | — | Schedules, sensitivity | 2 decimals for money |
| — | — | CSV/JSON exports | Plain CSV; UTF‑8 JSON |
Calculations run in your browser. No balances or schedules are sent to a server.