All-in-One Online Calculator & Converter Hub

Free Online Calculators for Finance, Health, Math & More

CalcMulti is a free, all-in-one online calculator platform covering finance, health, math, statistics, algebra, unit conversion, developer tools, and more. Every tool runs entirely in your browser — no login, no downloads, and no data collected. Whether you are calculating your mortgage payment, checking your BMI, solving a quadratic equation, converting currencies, or planning for retirement, CalcMulti delivers accurate results in seconds with clear, step-by-step explanations wherever possible.

All calculators are updated annually for 2026 tax tables, IRS rules, BLS salary data, and current interest rate assumptions. We publish detailed methodology notes and cite primary sources — BLS, IRS, CDC, and peer-reviewed formulas — so you can trust the numbers you get.

Financial Calculators

Our finance category includes over 40 tools covering mortgages, loans, investments, taxes, retirement planning, salary analysis, and cryptocurrency. The Mortgage Calculator computes monthly payments, total interest, and amortization schedules for any loan term and rate. The Salary Calculator converts hourly wages to annual pay — instantly answering questions like "$25 an hour is how much a year" ($52,000) or "$18/hr annually" ($37,440) — with adjustments for holidays and vacation days.

Retirement planning tools include the RMD Calculator (updated for SECURE 2.0 Act age changes), the Retirement Calculator with Fidelity savings benchmarks by age, and the FIRE Calculator for early retirement planning using the 4% rule. Tax tools cover federal income tax, capital gains, VAT for 27 EU countries, and state-level calculations.

Health & Wellness Calculators

Track your fitness, nutrition, and reproductive health with science-based tools. The BMI Calculator and Body Fat Calculator give you a clear picture of body composition. The TDEE Calculator and Macro Calculator use the Mifflin–St Jeor and Harris–Benedict equations to personalise your calorie and protein targets.

Fertility and pregnancy tools include the Ovulation Calculator, Due Date Calculator, Pregnancy Week Calculator, and luteal phase tracker — all designed for those planning or monitoring a pregnancy. Every health tool cites its source formula and includes an interpretation guide.

Math Calculators

From basic arithmetic to advanced functions, our math tools cover every level. The Fraction Calculator shows step-by-step solutions for addition, subtraction, multiplication, and division of fractions — including mixed numbers. The Percentage Calculator handles all three percentage problem types: what is X% of Y, X is what percent of Y, and percentage change. The Logarithm Calculator and Quadratic Equation Solver include full worked solutions and formula explanations for students and professionals alike.

Statistics Calculators

Our statistics suite covers descriptive statistics, hypothesis testing, probability distributions, and regression analysis — over 30 calculators in total. The T-Test Calculator supports one-sample, two-sample, and paired tests with p-value output. The Confidence Interval Calculator works for proportions and means at any confidence level. The Normal Distribution Calculator and Linear Regression Calculator are widely used by students, researchers, and data analysts. Every result includes an interpretation guide so you understand what the output means in practical terms.

Algebra Calculators

The algebra category offers 18 calculators and guides covering the core high-school and undergraduate curriculum. Solve quadratic equations with the Quadratic Formula Calculator — it shows the discriminant, both roots, and the full working. Factor polynomials with the Factoring Calculator, solve simultaneous equations with the System of Equations Calculator, and perform matrix operations including inverse and determinant. Companion guides explain the underlying theory so you can learn, not just compute.

Developer Tools & Unit Converters

Developers can format, validate, and transform data with 18 browser-based tools — no server required. The JSON Formatter pretty-prints and validates JSON instantly. The JWT Decoder parses header, payload, and signature without sending data to any server. Other popular tools include Base64 converter, URL encoder/decoder, hash generator, UUID generator, regex tester, and password generator. Our unit converter collection spans 12 measurement types — length, weight, temperature, area, volume, speed, pressure, energy, data storage, fuel economy, power, and time — with instant two-way conversion between all common units in metric and imperial systems.