Calculator
Formula used
- Gross interest: I = balance × rd
- Tax on interest: tax = I × taxRate
- Fee (annualized): fee = balance × (annualFee / dayCount)
- Net update: balance += (I − tax) − fee
How to use this calculator
- Enter your starting principal and annual rate.
- Choose rate type and day count basis.
- Set dates or use a duration in days.
- Add optional contributions, then pick timing.
- Include taxes, fees, and inflation if needed.
- Press Calculate to view results above the form.
Example data table
| Period | Balance | Gross Interest (Total) | Tax (Total) | Fees (Total) | Contributions (Total) |
|---|---|---|---|---|---|
| 2026-01 | 11,016.44 | 86.92 | 8.69 | 4.61 | 100.00 |
| 2026-03 | 11,281.33 | 260.78 | 26.08 | 13.95 | 300.00 |
| 2026-06 | 11,700.58 | 578.05 | 57.80 | 31.56 | 600.00 |
| 2026-12 | 12,532.10 | 1,306.40 | 130.64 | 72.70 | 1,200.00 |
Daily rate conversion and day-count impact
Nominal APR is divided by 365 or 360 to estimate the daily rate. At 10% APR, 365 basis gives about 0.0274% per day, while 360 gives about 0.0278%. That small gap compounds: over 365 days, the implied APY rises from roughly 10.52% to about 10.55%. Use 365 for most savings products and 360 for certain money‑market and loan conventions. On 50,000, that difference is roughly 15 to 20 over a year, and larger over multi‑year periods. Always match the basis used by your statement before exporting results for audit trails.
Contribution timing and cash-flow frequency
Regular deposits can dominate outcomes when compounding is daily. A 100 monthly contribution adds 1,200 in a year, but timing matters: start‑of‑day deposits earn one extra day of interest. Weekly or biweekly schedules smooth volatility in earned interest because the balance grows earlier. Quarterly deposits create step changes that are easy to audit in the schedule table.
Tax and fee drag on compounded returns
Taxes reduce interest each day, not just at year end, so the effective growth rate falls immediately. If daily interest is 3.00 and tax is 10%, only 2.70 is reinvested. Annual fees are converted to a daily charge on the balance; a 0.50% fee is about 0.00137% per day on a 365 basis. These drags compound too, so compare fee scenarios before choosing products.
APY, CAGR, and scenario comparison
APY reflects daily compounding without cash flows, while CAGR in this report compares final balance to total deposits across the period. When contributions are large, CAGR may look lower even as wealth increases. Use the schedule view to validate turning points and reconcile totals for gross interest, taxes, and fees. Export CSV to run side‑by‑side scenarios in a spreadsheet.
Inflation-adjusted outcomes and planning ranges
Inflation reduces purchasing power, so the calculator reports an inflation‑adjusted final value using the annual inflation rate. If inflation is 5% and the period is one year, a 12,000 nominal balance is worth about 11,429 in today’s terms. Try multiple durations to see sensitivity: 90 days highlights short‑term effects, while 1,825 days shows long‑run compounding. Use conservative inputs to stress test goals.
FAQs
Does the calculator assume constant interest rates?
Yes. It applies the same daily rate for every day in the period. To model rate changes, run separate date ranges with new rates and compare outputs using the CSV export.
What is the difference between nominal APR and effective annual rate?
Nominal APR divides the yearly rate by the selected day count to get a daily rate. Effective annual rate is converted to an implied daily rate so that compounding over the year matches the stated effective return.
How are contributions applied in the schedule?
Contributions are added by your chosen frequency: daily, weekly, biweekly, monthly, or quarterly. Timing controls whether the deposit is added before interest and fees (start of day) or after them (end of day).
Why can net interest or profit look low?
Taxes and annual fees reduce compounding because they are applied throughout the period. Large contributions increase total deposits, so profit versus deposits may shrink even while the final balance rises.
How is inflation-adjusted final value computed?
The calculator discounts the nominal final balance by the inflation rate across the period. It uses an annual inflation rate and scales it by the number of days to estimate today’s purchasing-power value.
Which schedule view should I choose?
Daily view is best for short ranges and auditing exact cash-flow days. Monthly or yearly views summarize long periods, keep tables readable, and still show cumulative interest, taxes, fees, and contributions.
- CSV export uses the latest calculated schedule from this session.
- PDF export captures the results section as a report.
- This tool is for estimation and education, not advice.