Everyday Money Math Calculators

10 calculators · 5 guides

This hub is for the quick sums that come up in everyday money decisions, before you need a specialist tool. It pulls together the Calcumetrics calculators for the core formulas: simple interest, compound interest, the interest rate hidden in a loan or deposit, and the effect of inflation on what money will buy.

Time-value tools let you move money across years. The future value calculator shows what an amount grows to, the present value calculator shows what a future sum is worth today, and the savings goal calculator works out how much to set aside each month to reach a target. For percentages in buying and selling, the profit margin, markup versus margin and ROI calculators answer the questions that trip people up most, such as why a 50% markup is not a 50% margin.

Short guides explain the ideas behind the numbers, including APR versus APY, flat versus reducing interest, real returns after inflation and markup versus margin. The hub suits students, households checking a quote or a bank offer, and anyone who wants to see the working rather than trust a headline rate. Each calculator shows its formula and runs in your browser.

Interest basics

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Simple Interest Calculator

Calculate simple interest, maturity value, and compare directly with compound interest growth.

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Compound Interest Calculator

Calculate compound interest for any principal, rate, time, and compounding frequency.

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Interest Rate Calculator

Solve for the implied interest rate from principal, payment, time, and repayment inputs.

Guides

Money over time

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Inflation Calculator

Calculate the future purchasing-power impact of inflation over time.

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Future Value Calculator

Calculate the future value of a present amount or cash-flow series at a chosen growth rate.

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Present Value Calculator

Calculate the present value of a future cash flow using a chosen discount rate.

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Savings Goal Calculator

Calculate the amount to save regularly to reach a target savings goal.

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Percentages in buying and selling

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Profit Margin Calculator

Calculate gross, operating, and net profit margins from revenue and cost inputs.

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Markup vs Margin Calculator

Understand and convert between markup percentage and gross margin for pricing decisions.

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ROI Calculator

Calculate return on investment as a percentage and annualised rate for any investment.

Guides

Markup vs. Margin: The Math Mistake That Silently Erases Business ProfitsLearn the exact mathematical difference between markup and margin, how to convert between them, and how confusing them leads to hidden business losses.

Frequently asked questions

What is the difference between simple and compound interest?

Simple interest is earned only on the original amount: interest = principal × rate × time. Compound interest is also earned on interest already added, so the balance grows faster the longer the money stays invested and the more often interest is compounded.

What is the difference between APR and APY?

APR is the annual rate before compounding. APY (or effective annual rate) includes compounding: APY = (1 + APR ÷ n)^n − 1, where n is the number of compounding periods a year. Monthly compounding at 12% APR gives about 12.68% APY.

How does inflation change the value of money?

At a constant inflation rate i, an amount today needs to grow to amount × (1 + i)^years to buy the same things later. At 6% inflation prices roughly double in 12 years.

How do I calculate a percentage return?

Return % = (final value − amount invested) ÷ amount invested × 100. To compare investments held for different lengths of time, convert it to an annual rate with the CAGR formula.