What does this interest calculator estimate?

It estimates future balance, total interest, total contributions, APY, after-tax interest, inflation-adjusted value, and a yearly growth schedule from the inputs you provide.

What is the difference between simple and compound interest?

Simple interest applies the rate only to the original principal. Compound interest adds earned interest back to the balance, so future interest can be earned on prior interest.

Why does APY differ from the stated interest rate?

APY reflects compounding frequency. With the same stated annual rate, more frequent compounding produces a slightly higher effective annual yield.

Should I include tax and inflation?

Use tax and inflation inputs when you want a more conservative estimate of purchasing power. Leave them at 0 for a quick nominal balance estimate.

Can this calculator predict investment returns?

No. It applies a fixed rate assumption. Real investments can rise or fall, rates can change, and fees or taxes can vary.

Savings and investment growth calculator

Interest Calculator

Estimate how money may grow with simple interest, compound interest, recurring contributions, taxes, and inflation. The calculator shows the formula, APY, and a year-by-year schedule so the result is easier to audit.

Enter your assumptions

Compound interest Simple interest

Initial principal Annual interest rate (%) Time length Compound frequency Monthly contribution Annual contribution Contribution timing Tax rate on interest (%) Inflation rate (%)

Results update automatically. No information is saved or sent to a server.

Estimated future balance $0.00

Enter your assumptions to estimate future value.

Total interest $0.00

Total contributions $0.00

Effective APY 0.00%

Inflation-adjusted value $0.00

Formula used

A = P(1 + r / n)^(n x t), plus recurring contributions.

Tax and purchasing power note

Tax and inflation assumptions are optional planning adjustments.

Growth schedule

The chart separates your starting principal and contributions from estimated interest. The table is yearly to keep the page readable on mobile.

Year	Start balance	Contributions	Interest	End balance

How to use this interest calculator

Enter the amount you already have saved as the initial principal.
Enter the annual interest rate or expected return as a percentage.
Choose compound interest for most savings, CDs, and investment growth estimates. Choose simple interest only when interest does not earn more interest.
Add monthly or annual contributions if you plan to keep depositing money.
Use tax and inflation only when you want an after-tax or purchasing-power view of the result.

Interest formula and calculation method

The standard compound interest formula is:

A = P(1 + r / n)^(n x t)

In this formula, A is the ending balance, P is principal, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is time in years. This calculator also simulates recurring monthly and annual contributions so deposits can grow after they are added.

For simple interest, the base formula is:

Interest = principal x annual rate x time

Simple interest is useful for a quick arithmetic check, but many real savings products and investments use compound growth. Lender and bank disclosures may use APR, APY, or other terms, so always compare the same type of rate.

What makes interest estimates easy to misread

An interest estimate is only as reliable as the assumptions behind it. A fixed 5% rate means the calculator applies that rate every year. A real savings account rate can change, while investment returns may be uneven or negative in some years.

Recurring contributions also change the interpretation. If you contribute every month, the final balance is not only the return on the original principal. It is the combined result of principal, new deposits, and growth on money added at different times.

Tax and inflation can materially reduce the useful value of interest. Nominal growth answers "how many dollars might I have?" Inflation-adjusted growth asks a different question: "what might those dollars be worth in today's purchasing power?"

Practical examples

Emergency savings

A household with $5,000 saved and $250 monthly deposits can estimate whether a high-yield savings account gets them closer to a six-month cash reserve.

Certificate of deposit comparison

A CD shopper can compare a stated annual rate with APY and see how compounding frequency changes the ending balance over a fixed term.

Long-term contribution plan

A saver can test how much of a future balance comes from their own deposits versus interest growth, then decide whether the monthly contribution is realistic.

APY, compounding, tax, and inflation

APY: Annual percentage yield includes compounding. If two accounts have the same stated rate but different compounding schedules, APY helps compare them more fairly.

Contribution timing: Beginning-of-period deposits usually produce a slightly higher result because the money has more time to earn interest.

Tax: Interest income may be taxable depending on the account, security, jurisdiction, and your personal situation. This calculator applies tax only to estimated interest, not to principal or contributions.

Inflation: Inflation does not reduce the number of dollars in the account, but it can reduce what those dollars buy. The inflation-adjusted value is an estimate of purchasing power, not a bank balance.

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Method, assumptions, and limitations

This calculator uses a fixed annual rate and user-entered compounding frequency. For compound interest with contributions, it converts the stated rate into an effective monthly growth path so monthly and annual deposits can be included in the schedule.

It does not pull live bank rates, brokerage returns, CD offers, tax brackets, inflation data, fees, or account rules. It does not model market volatility, changing rates, withdrawal penalties, account minimums, or deposit timing that differs from the selected assumptions.

Last reviewed: July 1, 2026. Editorial note: CalcToolBox shows formulas, assumptions, and limitations on the page so users can inspect the method instead of relying on a hidden calculation.

FAQ

Is compound interest always better than simple interest?

For a saver, compound interest usually produces a higher balance because earned interest can earn more interest. For a borrower, compounding can increase the cost of debt. The meaning depends on whether you are earning or paying interest.

What compounding frequency should I choose?

Use the frequency stated by the bank, CD, bond, or account disclosure. If you are making a rough estimate and do not know the exact rule, monthly compounding is a common default for planning.

Why does the schedule use yearly rows instead of every month?

Yearly rows make the schedule easier to scan and reduce page length, especially on mobile. The calculation still estimates growth with monthly contribution timing.

Does this calculator include fees?

No. If an account or investment charges a fee, reduce the expected rate or subtract the fee separately. Fees can meaningfully change long-term results.

Can I use this for loans?

You can use it to understand interest growth, but loan repayment needs amortization math. For loan payments, use the Mortgage Calculator or Auto Loan Calculator.

This calculator is for general informational purposes and simple arithmetic checks. It is not financial, tax, legal, investment, banking, or lending advice. Verify rates, compounding rules, taxes, fees, inflation assumptions, and account terms with qualified professionals and official disclosures.