How does compounding frequency affect returns?

More frequent compounding (daily > monthly > annually) results in slightly higher returns at the same nominal rate.

What is the Rule of 72?

Divide 72 by the annual interest rate to estimate years to double. At 6%, money doubles in roughly 12 years.

What is effective annual rate (EAR)?

EAR is the true annual return accounting for compounding. Monthly 6% APR gives EAR = (1+0.06/12)^12−1 = 6.168%.

Can I use this for loan interest?

Yes — enter the loan amount and rate. The total interest shows total cost over the term. For amortised loans use the Loan Calculator.

Finance

Simple & compound interest calculator

Enter your principal, annual rate, time period, and optional regular contributions to see future value, total interest earned, effective rate, and a year-by-year growth chart. Supports all compounding frequencies and 8 currencies.

Simple & compound interest Future value Regular contributions All compounding frequencies Year-by-year chart 8 currencies

Interest Calculator

Simple & compound interest with growth chart

Interest Type

Currency

Initial Principal

Annual Interest Rate

% / year

Time Period

Compounding Frequency

Regular Contributions (optional)

Future Value

—

Total interest

—

Principal

—

Contributions

—

Effective rate

Breakdown

Principal

Contributions

Interest

Year-by-Year Growth

Year	Balance	Interest	Contributions

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Interest Calculator — Simple & Compound Interest

This free interest calculator estimates the future value of a lump sum or a series of contributions using either simple interest or compound interest. It is useful for savings projections, investment analysis, deposit account comparisons, and understanding the long-term cost of debt.

Enter your starting principal, annual interest rate, time period (in years or months), and any regular monthly or yearly contributions. Choose simple or compound interest, select compounding frequency, and click Calculate for instant results with a year-by-year growth chart.

Interest Formulas

Simple Interest

I = P × r × t
A = P + I = P(1 + rt)

P = Principal · r = Annual rate (decimal) · t = Time (years)

Interest is calculated on the original principal only. Each period earns the same flat amount regardless of accumulated interest.

Compound Interest

A = P(1 + r/n)^nt

n = Compounding periods per year · t = Time (years)
With contributions: add FV of annuity to A

Interest is calculated on principal plus all previously earned interest. The more frequent the compounding, the faster the growth.

Effect of Compounding Frequency

How $10,000 at 5% APR grows after 10 years — compounding frequency only:

Frequency	n	Future Value	Interest Earned
Simple Interest	—	$15,000.00	$5,000.00
Annually	1	$16,288.95	$6,288.95
Semi-Annually	2	$16,386.16	$6,386.16
Quarterly	4	$16,436.19	$6,436.19
Monthly	12	$16,470.09	$6,470.09
Daily	365	$16,486.65	$6,486.65

The Rule of 72 — Quick Doubling Time

A simple shortcut for estimating how long it takes money to double at a given interest rate: divide 72 by the annual interest rate.

Years to double ≈ 72 ÷ Interest Rate (%)

3%≈ 24 years to double

6%≈ 12 years to double

9%≈ 8 years to double

12%≈ 6 years to double

Frequently Asked Questions

Simple interest is calculated only on the original principal each period. Compound interest is calculated on the principal plus all previously accumulated interest — so interest earns interest. For the same rate and time, compound interest always produces a higher final balance than simple interest.

More frequent compounding means interest is added to the balance more often, giving the new total more time to earn interest. Daily compounding produces the highest returns, but the practical difference between monthly and daily is small for most rates and time frames. Annually produces the least growth for compound interest.

The calculator adds the future value of an annuity to the lump-sum growth. For monthly contributions with compound interest, each contribution is compounded for the remaining periods. For simple interest, contributions earn flat interest on the portion of time remaining. The "contributions total" stat shows the raw amount you put in excluding the initial principal.

EAR is the actual annual return taking compounding into account. For monthly compounding at 6% APR, EAR = (1 + 0.06/12)¹² − 1 = 6.168%. For simple interest, EAR equals the nominal rate. The "effective rate" stat in the result always shows EAR.

Yes — enter the loan principal and rate. The "total interest" result shows how much interest accrues over the term. For amortised loan repayments (fixed monthly payments), use the Loan Calculator or Mortgage Calculator which handle amortisation schedules.

The Rule of 72 is a shortcut: divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 6%, money doubles in roughly 72 ÷ 6 = 12 years. It's most accurate for compound interest between 6% and 10%.

USD ($), EUR (€), GBP (£), JPY (¥), CAD (C$), AUD (A$), KRW (₩), and INR (₹). The selected symbol appears on the principal input and all result values. JPY and KRW are rounded to whole numbers.

The calculator uses standard financial formulas and is mathematically exact for the given inputs. Real-world returns vary due to variable rates, fees, taxes, and inflation. The projections assume a constant annual rate and consistent contributions throughout.

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