Compound Interest Calculator
Project your investment growth over time
Best for: Fixed deposits, savings accounts, bonds, or any lump-sum investment where you want to project future value.
Growth Visualization
🎥 How It Works
How to use the Compound Interest Calculator
Compound interest is the reason small savings turn into real wealth. Each time your balance earns interest, that interest itself starts earning interest. This calculator lets you project how a lump sum grows over any horizon with daily, monthly, quarterly, or annual compounding.
Step by step
- Principal Amount — the money you deposit today. Use your actual balance, not a target.
- Annual Interest Rate — the advertised rate on the account. Enter 8 for 8%, not 0.08.
- Time Period — how many years you’ll let the balance sit untouched.
- Compounding Frequency — how often interest is credited. Monthly is typical for savings accounts; daily for some high-yield accounts; annual for many bonds.
Press Calculate and the tool shows the final balance, total interest earned, and a growth chart. The table underneath breaks each year into opening balance, interest, and closing balance so you can verify the math by hand if you want to.
Why it’s important
Compounding rewards patience. Doubling the time usually produces far more than double the result, because the interest-on-interest effect accelerates. A handy shortcut is the Rule of 72: divide 72 by your rate to estimate years to double. At 8%, money doubles in roughly nine years; at 12%, in six.
Worked examples
Run a few scenarios before you lock your money into a long-term deposit — you may decide to stretch the horizon by just one more year.
Real-life scenario: saving for a child’s college
Imagine you open a savings account the day your daughter is born and deposit $10,000 earmarked for her college. At 7% compounded monthly, that single deposit grows to about $35,200 by her 18th birthday — more than triples without you adding a cent. Start eight years later and the same deposit only reaches about $17,800; the head start almost doubles the final number. This is why financial planners repeat the same line to every new parent: open the account today, automate a top-up, and let compounding carry the rest.
The same reasoning applies to retirement, an emergency fund, or any long-term savings goal. Plug in the target corpus you’ll need on day one of retirement, and work backward — the calculator turns an abstract “someday” goal into an exact monthly or one-time number you can act on today.
How the math works: the compound interest formula
The compound interest calculator uses the standard future-value formula:
A = P × (1 + r/n)n·t
where A is the final amount, P is the principal (initial deposit), r is the annual interest rate written as a decimal, n is the number of compounding periods per year (12 for monthly, 4 for quarterly, 365 for daily), and t is the number of years. The interest earned by itself is simply A − P.
Worked example. Deposit $10,000 (P) at 7% annual (r = 0.07), compounded monthly (n = 12) for 18 years (t = 18). The inner term is 1 + 0.07/12 = 1.005833…, raised to the 12 × 18 = 216th power gives roughly 3.5199. Multiply by the $10,000 principal and you end at $35,199.44, of which $25,199.44 is pure interest. Compounded daily instead of monthly, the final amount ticks up only about $40 — a useful reminder that the rate matters far more than the compounding frequency.
The calculator also supports simple interest via the toggle: that switches the formula to A = P × (1 + r·t), which ignores interest-on-interest and always produces a lower number for positive t. Use simple interest to model short-term bonds or certain loan structures where the lender explicitly does not compound.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is calculated only on the original principal, so it grows in a straight line. Compound interest earns interest on both the principal and all previously earned interest, so growth accelerates over time. Over 10 years at 8%, $10,000 becomes $18,000 under simple interest but $21,589 under annual compounding — a $3,589 difference that widens every additional year.
How often should interest compound for the best return?
More frequent compounding always beats less frequent at the same rate, but the difference is smaller than most people expect. At 10% annual for 10 years on $10,000, annual compounding yields $25,937, monthly $27,070, and continuous $27,183. The extra $100-$200 per year is real but shrinks as rates fall.
Does this calculator handle recurring deposits?
This version models a one-time lump sum. For monthly or recurring contributions, use the SIP calculator, which applies the future-value-of-annuity formula and accepts a monthly contribution amount alongside the initial deposit.
Is the result pre-tax or post-tax?
Pre-tax. Interest income is usually taxable in the country where the account is held — at your marginal tax bracket in most cases. Subtract an estimate of tax drag (commonly 15-30%) from the interest figure to approximate after-tax growth.