Free Online Compound Interest Calculator

Compound Interest Calculator

Calculate your investment growth with or without regular contributions, adjust advanced settings for precision.


Compound Interest Calculator: a friendly guide

If you’ve ever put money in a jar and felt… nothing happens—compound interest is the exact opposite of that. It’s your money earning interest, and then that interest also earning more interest. Over time, the growth starts to snowball. This page is your easy guide to using the Compound Interest Calculator on your tool page so you can see that snowball in action and make smarter money decisions.

What is compound interest?

Compound interest is interest on interest. You start with a principal (your starting amount). After a period, interest is added. Next period, you earn interest on the new total—principal plus the interest you already got. Repeat that many times and the curve bends upward.

Quick example:

If you invest $1,000 at 8% per year for 3 years, compounded annually:

After 3 years you’ll have about $1,259.71 (that’s ~$259.71 in interest).

Formula lovers: 

A = P (1 + r/n)^(n × t)

You don’t need to do this math by hand though—the calculator does it for you.

What this calculator can do

Your Compound Interest Calculator lets you:

  • Run Basic calculations (one-time deposit) or add regular contributions (like adding money monthly).
  • Choose compounding frequency: annually, semi-annually, quarterly, monthly, weekly, or daily.
  • Toggle Advanced Options to adjust for inflation and tax (handy if you want a more realistic, after-tax, after-inflation view).
  • See a Calculation Summary, a Growth Chart, and a Year-by-Year Breakdown.
  • Print results or Export PDF for your records. 

Step-by-step guide (super simple)

A) Basic (no regular contributions)
  1. Open the Basic tab.
  2. Enter Principal Amount ($) — your starting balance.
  3. Enter Annual Interest Rate (%) — e.g., 7 or 8 (no need to type the % sign).
  4. Enter Investment Period (Years) — how long you’ll invest.
  5. Pick a Compounding Frequency — annually, semi-annually, quarterly, monthly, weekly, or daily.
  6. (Optional) Click Show Advanced Options to set Inflation Rate (%) and Tax Rate (%) if you want a more realistic estimate.
  7. Hit Calculate.
  1. Review your Summary, Growth Chart, and Year-by-Year Breakdown. Use Print or Export PDF if you want to save or share the results. 
B) With Contributions (you add money regularly)

  1. Switch to the With Contributions tab.
  2. Fill in Principal Amount ($), Annual Interest Rate (%), Years, and Compounding Frequency.
  3. Enter your Contribution Amount ($) — the amount you’ll add each time.
  4. Choose Contribution Frequency — yearly, monthly, or weekly.
  5. (Optional) Open Advanced Options to apply Inflation and Tax.
  6. Click Calculate, then check the Summary, Chart, and Year-by-Year table. Again, you can Print or Export PDF. 

Tips that help:
  • If you’re saving from a paycheck, monthly compounding and monthly contributions feel most natural.
  • A higher compounding frequency can slightly boost growth (all else equal).
  • Use Inflation to estimate real (purchasing-power) growth, and Tax for a more accurate after-tax picture.

Mini glossary (so nothing feels confusing)

  • Principal: Your starting amount.
  • Rate (APR): The yearly interest rate.
  • Compounding: How often interest gets added to your balance.
  • Contributions: Extra deposits you add over time (weekly, monthly, yearly).
  • Inflation: Rising prices that reduce future purchasing power.
  • Tax: The bite taken from your interest earnings (if applicable).

FAQ

1) Does compounding frequency really matter?

A bit, yes. More frequent compounding (e.g., monthly vs. annually) means interest is added more often, which can slightly increase your ending balance—especially over long periods.

2) Should I use the Advanced Options?

If you want a real-world view, yes. Tax helps estimate after-tax earnings, and Inflation shows what your future money might be worth in today’s terms. It’s great for planning.

3) Can I add money regularly?

Absolutely. Use the With Contributions tab, enter a Contribution Amount, and pick Yearly / Monthly / Weekly. The calculator will factor in those deposits plus compounding. 

Final thought

Think of compound interest like rolling a snowball downhill—the longer it rolls and the more snow (contributions) you add, the bigger it gets. Use the calculator to test different “what ifs” and build a plan that fits your life.
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