Calculator Inputs
Formula Used
This calculator supports monthly compounding and produces gross, net, and inflation-adjusted views.
Monthly rate from nominal annual rate
Monthly Rate = Nominal Annual Rate / 12
Gross APY
APY = (1 + Monthly Rate)^12 - 1
Net monthly rate after tax
Net Monthly Rate = Monthly Rate × (1 - Tax Rate)
Net APY after tax
Net APY = (1 + Net Monthly Rate)^12 - 1
Inflation-adjusted ending value
Real Ending Value = Ending Balance / (1 + Inflation Rate)^(Months / 12)
Each month, the calculator applies contributions, interest, taxes on interest, and fees in sequence. Contribution timing changes whether deposits earn interest that same month.
How to Use This Calculator
- Enter your starting balance.
- Choose whether you are entering a nominal annual rate or a monthly effective rate.
- Add the number of months for your savings plan.
- Enter your monthly contribution amount.
- Select whether contributions happen at the beginning or end of each month.
- Include monthly account fees, if any.
- Add the tax rate applied to earned interest.
- Optionally enter inflation to see a purchasing-power view.
- Press the calculate button to show the result above the form.
- Review the chart, schedule, CSV export, and PDF export.
Example Data Table
| Initial Balance | Nominal Annual Rate | Months | Monthly Deposit | Tax Rate | Monthly Fee | Gross APY | Approx. Ending Balance |
|---|---|---|---|---|---|---|---|
| $5,000.00 | 4.50% | 12 | $100.00 | 10.00% | $1.00 | 4.5939% | $6,416.60 |
| $10,000.00 | 6.00% | 24 | $250.00 | 15.00% | $2.00 | 6.1678% | $17,323.62 |
| $20,000.00 | 7.50% | 36 | $400.00 | 20.00% | $4.00 | 7.7633% | $39,510.71 |
These rows are illustrative examples for quick comparison.
Frequently Asked Questions
1) What is APY?
APY means annual percentage yield. It reflects how compounding grows your money over a full year, not just the stated nominal rate.
2) Why does monthly compounding matter?
Monthly compounding credits interest more often than annual compounding. That increases the effective yearly yield because each month’s interest can earn interest later.
3) What is the difference between APY and APR?
APR usually describes a nominal annual rate without showing compounding impact. APY includes compounding, so it better represents the actual annual return.
4) Can monthly fees reduce APY results?
Yes. Monthly fees reduce ending balance and total gain. Even a small recurring fee can noticeably cut effective performance over longer periods.
5) Why include taxes on interest?
Taxes reduce the interest you keep. A gross APY can look attractive, but after-tax returns may be much lower depending on your tax rate.
6) What does inflation-adjusted ending value mean?
It estimates purchasing power after inflation. Your balance may grow in dollars while buying power grows more slowly, stays flat, or even falls.
7) When should I choose beginning-of-month contributions?
Choose beginning-of-month contributions when deposits are made before interest is credited. Those deposits then participate in that month’s compounding.
8) Can I enter zero or negative inflation?
Yes. Zero inflation shows nominal purchasing power. Negative inflation models deflation, which can increase the real value of future money.