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Hazuu Tools

Interest Rate Calculator

Calculate simple interest, compound interest, and compare investment growth scenarios.

savingsInterest Rate Calculator
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Interest Details

Interest Type
Principal Amount
$
Interest Rate (%)
%
Time Period
Tax Rate (optional)
%
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Interest Summary

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Enter your principal amount and interest rate to see results
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About Interest Rate Calculator

The Interest Rate Calculator computes both simple interest and compound interest on any principal amount, returning the total interest earned, the future value of the investment, and the effective annual return rate. You choose between the two interest models, enter a principal, an annual rate, and a time period in years, months, or days — and for compound interest you also pick the compounding frequency (monthly, quarterly, semi-annually, or annually). Results appear instantly with a full calculation breakdown table.

Knowing exactly how much a deposit or savings account will grow is fundamental to comparing financial products. A 5% rate compounded monthly is meaningfully different from 5% compounded annually, and this calculator makes that difference explicit. It also accepts an optional income-tax rate so you can see the after-tax interest, the tax amount deducted, and the adjusted future value — figures you need when weighing interest income against your marginal tax bracket.

Every calculation runs entirely inside your browser using standard arithmetic — no data leaves your device, no account is required, and there are no usage limits. The tool is free to use as many times as you like for personal finance planning, homework, or quick back-of-the-envelope checks on any interest-bearing product.

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Key Features

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Simple and compound interest in one tool

Switch between the two models with a single click. Simple interest uses I = P x r x t; compound interest uses A = P x (1 + r/n)^(n*t), where n is your chosen compounding frequency.

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Four compounding frequencies

Monthly, quarterly, semi-annually, and annually — covering the most common savings account and certificate of deposit schedules so your results match the real product terms.

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Flexible time units

Enter the investment term in years, months, or days. The calculator converts automatically, making it accurate for short-term deposits, 90-day T-bills, or multi-year savings goals.

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After-tax return calculation

Enter an optional income-tax rate to see the tax amount on interest, the net interest remaining after tax, and the post-tax future value — useful when comparing taxable and tax-advantaged accounts.

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Effective annual return rate

Displays the true annual yield accounting for compounding. For simple interest this equals the nominal rate; for compound interest it is (1 + r/n)^n - 1, letting you compare products quoted at different frequencies on equal footing.

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Preset rate buttons

Common rates (2%, 3%, 4%, 5%, 6%, 8%) are available as one-click presets, with a free-entry field for any custom rate down to one decimal place.

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How to Use

01

Choose Interest Type

Select between Simple Interest and Compound Interest. Simple interest is calculated only on the principal amount, while compound interest is calculated on both the principal and accumulated interest.

02

Enter Details

Input your principal amount and annual interest rate. You can use the preset rate buttons for common rates or type a custom value. Optionally enter a tax rate to see after-tax returns.

03

Set Time Period

Enter the duration of your investment and choose the unit — Years, Months, or Days. For compound interest, also select the compounding frequency (Monthly, Quarterly, Semi-Annually, or Annually).

04

Calculate

Click Calculate Interest to see your interest earned, future value, effective annual return rate, and a complete calculation breakdown. If a tax rate is set, after-tax figures are also displayed.

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Example

Compound interest on $5,000 at 6% per year for 3 years, compounded monthly. The effective annual rate accounts for monthly compounding.

Inputs
Principal:            $5,000.00
Interest Type:        Compound
Annual Rate:          6%
Time Period:          3 Years
Compounding:          Monthly (12x/year)
Tax Rate:             0%
Results
Interest Earned:      $983.40
Future Value:         $5,983.40
Effective Annual Rate: 6.17%

Calculation: $5,000 x (1 + 0.06/12)^(12x3)
           = $5,000 x (1.005)^36
           = $5,983.40
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Common Use Cases

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    Comparing savings account offers

    Banks advertise the same nominal rate at different compounding frequencies. Enter each offer and compare the effective annual rate and future value to find which account actually pays more over your deposit term.

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    Estimating after-tax interest income

    Interest from savings accounts and certificates of deposit is taxable income. Enter your marginal tax rate alongside the deposit terms to see your real net return before committing to a product.

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    Evaluating fixed-deposit or bond terms stated in days

    Short-term instruments like 90-day T-bills or 6-month term deposits are quoted in days or months, not calendar years. Switch the time unit to days or months to get an accurate future value without manual unit conversion.

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    Teaching yourself how compounding works

    Run the same principal and rate as both simple and compound to see the concrete dollar difference that compounding frequency makes over 1, 5, and 10 years — a direct comparison that textbook formulas rarely show side by side.

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    Quick verification of bank or broker statements

    If a bank statement shows an unexpected interest credit, enter the stated principal, rate, and days elapsed to recalculate independently and confirm the figure is correct.

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Frequently Asked Questions

What is the difference between simple and compound interest? expand_more
Simple interest is calculated only on the original principal amount. The formula is I = P x r x t. Compound interest is calculated on both the principal and the accumulated interest from previous periods, using the formula A = P x (1 + r/n)^(n*t). Over time, compound interest grows faster because you earn interest on your interest.
How does compounding frequency affect returns? expand_more
The more frequently interest is compounded, the more interest you earn. For example, monthly compounding (12 times per year) produces a higher return than annual compounding (once per year) at the same nominal interest rate, because interest is added to the principal more often and begins earning additional interest sooner.
What is the tax rate field used for? expand_more
The optional tax rate field lets you estimate how taxes will reduce your interest earnings. When you enter a tax rate, the calculator shows the tax amount on your interest, the interest remaining after tax, and the adjusted future value. This helps you understand your real, after-tax return on investment.
How is the effective annual return rate calculated? expand_more
For simple interest, the effective annual return rate equals the nominal interest rate you entered. For compound interest, it is calculated as (1 + r/n)^n - 1, where r is the annual rate as a decimal and n is the number of compounding periods per year. This tells you the true annual yield accounting for compounding.
Can I calculate interest for periods in days or months? expand_more
Yes. You can enter your time period in Years, Months, or Days. The calculator converts months to years by dividing by 12 and days to years by dividing by 365. This is useful for short-term deposits, savings bonds, or any investment with a non-standard term length.
How is this different from the Loan Calculator or Mortgage Calculator on this site? expand_more
This Interest Rate Calculator works in the direction of growth: you have a lump sum today and want to know its future value at a given rate. The Loan Calculator and Mortgage Calculator work in the opposite direction — you have a debt and want to know the repayment schedule, monthly payment, and total interest paid over the life of the loan. Use this tool for deposits, savings, and investments; use those tools for borrowing and repayment planning.
What is the difference between the nominal rate and the effective annual rate? expand_more
The nominal rate is the interest rate as advertised (e.g. 6% per year). The effective annual rate (EAR) accounts for how often that rate is applied within the year. At 6% compounded monthly, the EAR is (1 + 0.06/12)^12 - 1 = approximately 6.17%. The more frequent the compounding, the higher the EAR relative to the nominal rate.
Can I use this to see how inflation erodes the real value of savings? expand_more
Not directly — this tool calculates nominal interest growth, not inflation-adjusted returns. To estimate real returns, you can run two calculations: one at your savings rate and one at the inflation rate, then compare the resulting future values to see whether your money is growing faster than prices.
Is this calculator accurate for continuous compounding? expand_more
Continuous compounding is not one of the four frequency options. The closest approximation is monthly compounding (12 periods per year), which produces a result very close to continuous compounding for most practical purposes. Continuous compounding uses the formula A = P x e^(r*t) and differs from monthly compounding by only fractions of a percent at typical savings rates.