CalcPlanet offers 725+ free online calculators and tools across finance, health, math, science, conversions, and everyday life. Use our BMI calculator, mortgage calculator, percentage calculator, loan EMI calculator, tip calculator, currency converter, salary to hourly converter, discount calculator, sales tax calculator, and hundreds more — all instant, mobile-friendly, and require no sign-up. Whether you need to calculate body mass index, monthly mortgage payments, percentage change, compound interest, calorie intake, unit conversions, or crypto prices, CalcPlanet provides accurate results with transparent formulas and step-by-step explanations. Our growing library of free calculators is trusted worldwide for finance planning, fitness tracking, academic study, engineering, cooking, travel, and small business. Explore curated guides, real-world examples, and formula references to learn how each calculation works. Browse popular categories: BMI calculator, percentage calculator, mortgage calculator, tools, all calculators, guides, formulas, finance, health, math, conversion, and about CalcPlanet. Free calculators, instant answers, no ads in core results, accurate every time.
Compound interest is the 8th wonder of the world. With this calculator you see exactly how your money grows exponentially over time.
Enter starting amount, annual interest rate, time period and optional monthly contributions for a complete growth overview.
The key difference between simple and compound interest: compound interest earns interest on your previously earned interest, creating exponential growth.
This calculator is most useful when making decisions where time horizon matters — choosing between paying off a low-rate debt versus investing the money, deciding how many years to extend an investment before withdrawing, or comparing two savings accounts with different compounding frequencies. It is also the right tool for visualising the cost of starting late: run the same monthly contribution starting at age 25 versus 35 and see how significant a 10-year delay really is.
The most pervasive mistake is overweighting compounding frequency relative to rate and time. Daily compounding on a 3% account does not remotely approach monthly compounding on a 4% account — rate dominates frequency in every realistic scenario. A second error is ignoring inflation when projecting long-term savings: £100,000 in 30 years is not £100,000 in today's purchasing power. Use the real return rate (nominal rate minus inflation) for meaningful long-term projections.
Someone invests £500/month from age 30 to 65 at a 6% annual return. Total contributions: £210,000. Final balance: approximately £591,000 — nearly £381,000 is interest earned on contributions alone. Now delay the start by 10 years: same £500/month from age 40, same rate. Total contributions: £150,000. Final balance: approximately £309,000. A £60,000 difference in contributions produces a £282,000 difference in outcome — that is the cost of waiting, and it is invisible without a compound interest calculator.
Compound Interest Formula
A = P × (1 + r/n)^(n×t)
Where A = final amount, P = principal, r = annual interest rate (decimal), n = compounding periods per year, t = time in years.
You invest
Result: $40,387 — your
Interest on interest. You earn interest on both your principal and previously accumulated interest, causing exponential growth.
More frequent compounding means more growth. Daily compounding earns slightly more than monthly, which earns more than annual.
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 8%, money doubles in ~9 years.
Simple interest only earns on the original principal. Compound interest earns on the principal plus all accumulated interest.
Free, fast, and easy. Use 722 calculators and 108 tools. No sign-up. Get instant results for math, money, health, and more.
By CalcPlanet Editorial · · According to our Editorial Standards and Formula Sources, every calculator is reviewed before publication.
CalcPlanet calculators are free, privacy-first, and formula-reviewed.
Editorial Standards · Formula Sources · Privacy · Terms · Contact
