Calculate simple interest, compound interest, loan repayment and investment growth online free. See full breakdown. No sign-up. Runs in your browser.
Simple Interest
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Interest and Loan Calculator
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Frequently Asked Questions
Simple interest is calculated only on the original principal: Interest = P x R x T. Compound interest is calculated on the principal plus previously accrued interest: A = P x (1 + R/n)^(nT), where n is the number of compounding periods per year. For a $10,000 investment at 5% over 10 years, simple interest yields $5,000 while monthly compounding yields $6,470 — 29.4% more. Compound interest is why long-term investments grow exponentially rather than linearly.
Compounding frequency is how often the interest is calculated and added to the principal. Annual compounding adds interest once per year. Monthly compounding adds interest 12 times per year. Daily compounding adds interest 365 times per year. More frequent compounding means slightly higher effective returns. The difference between monthly and daily compounding is small for personal finance, but significant for large sums over long periods. Most savings accounts and mortgages use monthly compounding.
APR (Annual Percentage Rate) is the nominal annual interest rate without accounting for compounding. APY (Annual Percentage Yield) is the effective annual rate that accounts for compounding frequency. For a 6% nominal rate compounded monthly, the APY is (1 + 0.06/12)^12 - 1 = 6.168%. Lenders are required to disclose APR in many jurisdictions, but APY gives a more accurate picture of actual cost or earnings.
Loan payoff mode uses the EMI formula to calculate the monthly payment needed to fully repay the principal plus all interest over the specified tenure. It shows the total amount repaid, total interest paid, and monthly payment. This is equivalent to the EMI calculator but presented with the interest-versus-principal split. Use this to compare different loan offers by seeing total interest cost across the full repayment period.
Compound interest works in your favour when you are an investor (money growing in savings or investments) and against you when you are a borrower (debt growing if not repaid). Credit card debt typically compounds daily at high rates (15-30% APR), meaning unpaid balances grow very quickly. Understanding compound interest on both sides of the equation is fundamental to good personal financial management.
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Free Loan and Interest Calculator Online — Simple Interest, Compound Interest and Loan Payoff
Interest calculations underpin every financial product and investment decision. Whether you are comparing savings accounts, evaluating investment returns, understanding the true cost of a loan, or planning a mortgage, knowing how to compute simple and compound interest accurately is essential. The Loan and Interest Calculator on OneDocPDF covers all three common interest calculation scenarios: simple interest for short-term calculations, compound interest for investment and savings growth projections, and loan payoff for instalment repayment planning — all running instantly in your browser.
Albert Einstein is often attributed with calling compound interest the eighth wonder of the world, though the attribution is apocryphal. The sentiment, however, is grounded in mathematical reality. At 7% annual compound interest (the historical average real return of diversified equity portfolios), money doubles approximately every 10.2 years following the Rule of 72. A 25-year-old investing $10,000 and adding $500 monthly until age 65 at 7% annual return would accumulate approximately $1.3 million, of which only $250,000 represents actual contributions — the remaining $1.05 million is pure compound growth.
For related financial tools, see our EMI Calculator for detailed loan repayment scheduling with an amortisation table, our Discount Calculator for pricing calculations, and our Percentage Calculator for general proportional maths. All tools are free, private, and browser-based.