Modify the values and click the Calculate button to use
| Item | Total |
|---|---|
| Initial Principal | $0.00 |
| Total Contributions | $0.00 |
| Total Deposited | $0.00 |
| Interest Earned | $0.00 |
| Effective Annual Rate | 0.00% |
| Investment Term | - |
Yearly Growth Schedule
| Year | Starting Balance | Contributions | Interest | Ending Balance |
|---|
Simple and compound interest explained
Interest can be calculated on the original principal alone or on a growing balance that includes prior interest. Simple interest grows at a steady dollar amount. Compound interest can accelerate because each new period may earn interest on earlier interest as well as on deposits.
Use the calculator to separate money contributed from growth produced by the assumed rate. Change the compounding frequency and contribution timing to understand their effect, but remember that advertised investment returns are not guaranteed like a contractual savings rate.
How to use this calculator
- Enter the starting principal and the annual interest or return assumption.
- Choose simple or compound interest and select the compounding frequency.
- Set the time horizon and add regular contributions if you plan to make them.
- Compare the ending balance with total deposits to isolate estimated interest or growth.
How the calculation works
Simple interest is I = P x r x t. Compound growth without extra deposits is A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounding periods per year, and t is years. Contributions require a series calculation.
A practical example
$10,000 earning 5% simple interest for 10 years produces $5,000 of interest and a $15,000 balance. With annual compounding at the same stated rate, the balance is about $16,289. Monthly $100 contributions would increase deposits and the potential growth further.
How to use the result in a real decision
Separate guaranteed account terms from investment assumptions when using the result. For a bank product, confirm the APY, minimum balance, withdrawal rules, and how long the rate remains available. For an investment scenario, treat the ending balance as one possible outcome and test lower returns. Focus on the contribution habit, time horizon, costs, taxes, and risk rather than selecting a product only because a high assumed rate creates an attractive projection.
Ways to make the estimate more useful
- Use an annual percentage yield when comparing deposit accounts with different compounding schedules.
- For investments, test conservative, moderate, and optimistic return assumptions.
- Account for taxes, fees, and inflation when interpreting long-term growth.
- Regular contributions often matter more than small differences in compounding frequency.
Frequently asked questions
What is the difference between APR and APY?
APR states an annual rate without fully reflecting compounding, while APY reflects the compounding effect over a year.
Does more frequent compounding always help?
At the same nominal rate it can modestly increase growth, although fees, taxes, and the actual quoted APY may matter more.
Can compound interest produce losses?
A guaranteed positive deposit rate does not, but an investment return is uncertain and the account value can fall.
NumbersHub educational guide. Review calculator assumptions before relying on an estimate.