Calculate interest and ending balance with simple or compound interest, contributions, taxes and inflation.
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | $12,400.00 | $567.39 | $12,967.39 |
| 2 | $14,800.00 | $1,286.60 | $16,086.60 |
| 3 | $17,200.00 | $2,165.39 | $19,365.39 |
| 4 | $19,600.00 | $3,211.93 | $22,811.93 |
| 5 | $22,000.00 | $4,434.80 | $26,434.80 |
| 6 | $24,400.00 | $5,843.03 | $30,243.03 |
| 7 | $26,800.00 | $7,446.09 | $34,246.09 |
| 8 | $29,200.00 | $9,253.96 | $38,453.96 |
| 9 | $31,600.00 | $11,277.11 | $42,877.11 |
| 10 | $34,000.00 | $13,526.55 | $47,526.55 |
Please do not make financial decisions based on these results.
What is the Interest Calculator?
An interest calculator shows how much interest a deposit or loan balance earns over time, using simple or compound interest and optional regular contributions.
How investments grow
Growth depends on how much you invest, how long you stay invested and the rate of return. Because returns compound, time is the most powerful input. Start with the compound interest calculator to see the effect, then use the investment calculator for contributions and taxes.
How to use the Interest Calculator
- Enter your numbers. The inputs are Initial deposit ($), Interest rate (% per year), Time: years, Additional contribution ($). Use a rate of return you consider realistic; small changes compound into large differences. Fields marked optional can stay at zero.
- Choose your options. Interest type / compounding, Contribution frequency, Contributions are made at the… change how the result is worked out, and the form updates to match your choice.
- Read the result. The highlighted box gives the Ending balance, and the cards below show Starting amount, Total contributions, Total interest earned. Tables and charts break it down further.
- Test other scenarios. Results update as you type. Change one value at a time to see what drives the answer, and press Reset to go back to the defaults.
Formula and how it works
Example with real numbers
Here is the Interest Calculator using the default values shown in the calculator above:
Inputs
| Initial deposit ($) | 10,000 |
|---|---|
| Interest rate (% per year) | 5 |
| Time: years | 10 |
| Interest type / compounding | Monthly |
| Additional contribution ($) | 200 |
| Contribution frequency | Monthly |
| Contributions are made at the… | End of each period |
Results
| Ending balance | $47,526.55 |
|---|---|
| Starting amount | $10,000.00 |
| Total contributions | $24,000.00 |
| Total interest earned | $13,526.55 |
With these inputs the calculator returns Ending balance: $47,526.55. Change any value in the calculator to see how the result moves.
What the results tell you
The results panel of the Interest Calculator reports Ending balance, starting amount, total contributions and total interest earned. Compare these figures while changing one input at a time, and use the related calculators below to look at the same situation from another angle.
Tips for better results
Method and limits. This calculator applies the formula in the section above to your inputs, in your browser; nothing you enter is stored on our servers. Investment returns are not guaranteed. The result shows what the numbers you enter would produce, not what the market will do. It is for information, not financial, tax or legal advice.
Frequently asked questions
Simple vs compound interest?
Simple interest is earned only on the principal. Compound interest is also earned on past interest.
How is interest taxed?
Interest from savings and CDs is generally taxed as ordinary income. Enter your rate in the tax field to see the after-tax effect.
Are investment returns guaranteed?
No. Real returns vary. Use these tools to compare scenarios, not to predict results.
What rate of return should I assume?
There is no guaranteed rate. Test a range of conservative and optimistic rates, and remember that fees and inflation reduce your real return.
Are the results guaranteed?
No. Results depend entirely on the numbers you enter and the formulas shown on this page. Please do not make financial decisions based on them alone; confirm important figures with a licensed professional.
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