Calculate compound interest and total amount with adjustable compounding frequency (annual to daily). Free online compound interest calculator using A = P(1 + r/n)^(nt).
The Tooloogle Compound Interest Calculator computes the future value of an investment (or the total payable on a loan) using the standard formula A = P(1 + r/n)^(nt), where the compounding frequency n can be set to annual, semi-annual, quarterly, monthly, or daily. Enter principal, annual interest rate, time in years, and compounding frequency; see the total amount and the interest earned (or owed) immediately. Calculation runs in your browser; no signup, no upload.
Compound interest is interest that's calculated not just on the original principal, but also on the accumulated interest from previous periods. In a simple-interest world, a principal of 1,000 at 10% per annum yields 100 every year forever. In a compound-interest world, the same 1,000 at 10% compounded annually yields 100 in year one, then 110 in year two (because year two's interest is on 1,100), then 121 in year three, and so on — the gains accelerate over time. Albert Einstein reportedly called compound interest "the eighth wonder of the world"; whether he actually said it or not, the underlying math is responsible for the success of long-term savings plans, retirement accounts, fixed deposits, mortgages (where it works against the borrower), credit-card debt (which can spiral), bond yields, and most other financial instruments that span more than a year or two.
Live calculation — total and interest update as you change any input.
Five compounding frequencies — annually (1×), semi-annually (2×), quarterly (4×), monthly (12×, the default for most modern savings accounts), and daily (365×).
Sensible defaults — principal 1,000, rate 5%, time 1 year, monthly compounding are pre-filled so you see a working example without entering values first.
Decimal-friendly — rate accepts fractional percentages; time accepts half-year and quarter-year increments.
Two-decimal precision — results are rounded to cents.
Two results — total amount (principal plus interest) and interest earned (the amount the principal grew by) shown side by side.
Browser-only — calculation runs locally in JavaScript. No data is uploaded.
Enter the principal amount (the original sum invested or borrowed) in the "Principal Amount" field.
Enter the annual interest rate as a percentage (e.g. 5 for 5% per annum).
Enter the time period in years (e.g. 10 for ten years; 0.5 for six months).
Pick the compounding frequency from the dropdown — choose "Monthly" for most modern savings accounts, "Annually" for textbook problems, "Daily" for some high-frequency products.
Read the two results: total amount (what you'll have at the end) and interest earned (the gain over the principal).
Adjust any input to model different scenarios — what if I leave the money for 20 years instead of 10? what if the rate is 7% instead of 5%? what if I switch from annual to monthly compounding?
Personal-finance enthusiasts modelling retirement-savings growth and the long-term impact of starting early. Investors evaluating fixed deposits, bonds, and certificate-of-deposit (CD) products that use compound interest. Borrowers understanding the true cost of a multi-year loan with compounding interest charges. Mortgage holders modelling the accumulated interest paid over a 15- or 30-year term. Credit-card users seeing what carrying a balance at 18% APR really costs over a year, two years, five years (it's usually shocking). Educators and students working through compound-interest problems in finance, economics, and arithmetic curricula. Financial advisors illustrating the difference compounding frequency makes (annual vs monthly vs daily). Parents starting a children's savings plan and wanting to project the maturity value at age 18. Policy analysts modelling government debt projections at various interest rates over decades. Anyone wondering "how long will it take my savings to double?" — the rule of 72 (divide 72 by the annual rate) gives a rough answer; this calculator gives the exact answer.
The formula A = P(1 + r/n)^(nt) uses four inputs:
P = principal (the starting amount).
r = annual interest rate as a decimal (5% = 0.05). Expressed as a decimal because the rate field accepts whole-number percent and the formula divides by 100 internally.
n = number of compounding periods per year (1 = annual, 12 = monthly, 365 = daily).
t = time in years (can be fractional).
The output A is the total amount at the end of the period; the interest earned is simply A − P. The formula captures the essence of compounding: every period, your balance is multiplied by (1 + r/n), so over nt periods the multiplier is (1 + r/n)^(nt). As n grows (more frequent compounding), the result approaches the continuous-compounding limit P × e^(rt), which is the maximum possible compounding for a given annual rate. In practice, daily compounding is so close to continuous that the difference is negligible.
Example 1: 10-year savings. 10,000 at 6% per annum compounded monthly for 10 years. A = 10000 × (1 + 0.06/12)^(12×10) = 10000 × (1.005)^120 = 10000 × 1.8194 = 18,193.97. Interest earned: 8,193.97. Compare with simple interest at the same rate: 10000 × 6 × 10 / 100 = 6,000 of interest. Compound interest delivers 2,194 more — that's the "magic of compounding".
Example 2: 30-year retirement projection. 50,000 at 7% per annum compounded annually for 30 years. A = 50000 × (1.07)^30 = 50000 × 7.6123 = 380,613.16. Interest: 330,613.16. The principal more than 7×-es over three decades.
Example 3: Compounding frequency comparison. 1,000 at 10% per annum for 5 years. Annual compounding: 1,000 × (1.10)^5 = 1,610.51. Monthly: 1,000 × (1 + 0.10/12)^60 = 1,645.31. Daily: 1,000 × (1 + 0.10/365)^1825 = 1,648.39. The difference between monthly and daily is small (about 3); between annual and monthly noticeable (about 35). For most purposes, monthly compounding is a good approximation of higher frequencies.
This calculator models a single lump-sum principal growing under compound interest. It does not model regular contributions (e.g. "deposit 500 every month for 20 years") or withdrawals. For contribution-based projections (SIP, 401(k), retirement accounts that receive monthly deposits), the math is different (it's an annuity formula) and Tooloogle plans a separate Annuity / SIP Calculator for that case. To approximate periodic contributions, you can run this calculator multiple times with different start dates and add the results — tedious but workable for small numbers of contributions.
Always confirm the compounding frequency before evaluating a product — an "annual rate of 6% compounded monthly" produces a higher actual return than "6% compounded annually". The truer comparison metric is APY (Annual Percentage Yield) for savings or APR (Annual Percentage Rate) for loans — both account for compounding so two products with different frequencies can be compared fairly. The rule of 72 (divide 72 by the annual rate) approximates how many years it takes a sum to double under compound interest — at 6%, a sum doubles in about 12 years; at 8%, in about 9 years. For multi-decade projections, small rate differences compound into huge gaps — 6% over 40 years grows 10,000 to 103,000; 8% grows it to 217,000; the 2-percentage-point gap more than doubles the result. Inflation eats compound interest just as compound interest grows the principal — for real (after-inflation) projections, subtract the inflation rate from the nominal rate before using the calculator.
Calculation runs entirely in your browser using Math.pow. No principal, rate, time, or frequency value is uploaded; the financial scenarios you're modelling stay private. Verify with DevTools that no requests fire as you change inputs.
Tooloogle's calculator is focused: four inputs, two results, with a clear formula explainer below the tool for learners. No signup, no ads in the math, no upsell to a premium "portfolio modeller". The five-step compounding-frequency dropdown covers every common product convention from annual to daily. Pair this calculator with the Tooloogle Simple Interest Calculator (for side-by-side comparison) and the Percentage Calculator (for any percentage question that comes up while modelling). Bookmark the page; the next time you evaluate a savings product, a CD, a retirement projection, or a multi-year loan, the answer is four input fields away.
How to Use Compound Interest Calculator - Calculate CI with Formula Online
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Calculate compound interest and total amount with adjustable compounding frequency (annual to daily). Free online compound interest calculator using A = P(1 + r/n)^(nt).
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