Free Online Calculators for Everyday Math, Money, and Work
CalcAuthority is a free calculator resource covering the calculations ordinary people, students, workers, homeowners, and business owners reach for every day — percentages, salary and paycheck math, loans and mortgages, time and work hours, unit conversions, and business and construction figures. No black boxes and no signups: every serious tool shows its formula, states its assumptions, and explains the result in plain English.
Browse by Category
Pick a category to see every calculator it covers, or browse the full library.
Popular Calculators
Some of the most-used tools on CalcAuthority, across categories.
Everyday Essentials
Quick, high-frequency calculations that come up in everyday life — elapsed time, work hours, and rising fuel costs.
- Time Duration CalculatorCalculate elapsed time between a start and end time, with next-day handling.
- Work Hours CalculatorCalculate net work hours from clock-in and clock-out times, with an optional break deduction.
- Gas Cost Increase CalculatorFind out exactly what a gas price change costs you monthly and yearly based on your real driving.
The Method Behind Every Calculator
A calculator that just returns a number is a black box. Ours are built to show their work — the serious tools carry all five parts:
- The formula — stated in plain language
- The assumptions — what's given, what you supply
- Worked examples — verify it by hand
- How to read the result — what the number means
- Limitations — where the math stops
Full details on the Methodology page.
Business & Construction Calculators
CalcAuthority also runs a strong set of tools for owners, operators, and the trades — labor cost, job pricing, break-even, cash runway, and pricing decisions.
Transparent Formulas, Reviewed Content
General calculators on CalcAuthority use established, standard formulas, shown in full so you can verify the math yourself — nothing is hidden in a black box. The Construction & Trades tools are additionally informed by real field experience: CalcAuthority's founder and reviewing editor, Gerald G., is a journeyman cabinet installer who worked as a subcontractor and ran a contracting business with 18 employees. That field knowledge shapes the trade tools; the everyday math, money, and conversion calculators rest on the standard formulas each result cites. Read more about CalcAuthority and our Methodology.
Field Guides
Plain-English explanations of the math behind the tools — worked numbers, and where each calculation goes wrong.
How Our Calculators Work
Each serious calculator follows the same structure: an interactive tool, a How It Works section stating the formula, Worked Examples applying it to real numbers, guidance on what the result means and when to use it, and a FAQ. The Methodology page explains our formula, benchmark, and result-band policies. The Field Guides explain the reasoning behind the math.
Results are estimates for planning purposes only — not financial, tax, legal, or accounting advice. See our Financial Disclaimer.