Editorial principles
- Every formula and figure is verified against official sources (laws and public agency notices).
- When rates change, the calculator and its guide content are updated together.
- Reported errors are fixed as soon as they are confirmed.
Calculators by Sin Dongho (178)
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Health
Calorie Calculator
Calculate your daily calorie needs based on the Mifflin-St Jeor equation and USDA Dietary Guidelines activity factors. Get targets for weight loss, maintenance, or weight gain.
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Health
Body Fat Calculator
Free body fat percentage calculator using the US Navy circumference method (Hodgdon-Beckett, 1984). Validated within ±3–4% of hydrostatic weighing — the lab reference standard.
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Developer Tools
Regex Tester
Free online regex tester using PCRE syntax. Test match, find groups, and run replacement. Highlights matches in your test string with capture group breakdown.
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Education
SAT / ACT Score Calculator
Free SAT and ACT score calculator. Get your percentile, convert SAT to ACT (or vice versa) using the official 2018 College Board / ACT concordance, and see typical college score ranges.
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Health
Water Intake Calculator
Free water intake calculator based on the National Academies (NASEM/IOM) Adequate Intake recommendations: 125 oz/day for men and 91 oz/day for women, including water from food and beverages.
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Lifestyle
Percentage Calculator
Free percentage calculator with three modes: find X% of Y, find what percent X is of Y, and calculate percent change between two values. Plain-English explanation included.
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Lifestyle
Discount Calculator
Free discount calculator. Enter list price and percent off to instantly get sale price, dollars saved, and a visual price-vs-savings breakdown. Handles stacked discounts.
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Lifestyle
Date Calculator
Free date calculator. Find days, weeks, months, and years between two dates, or add and subtract days from a base date. Returns weekday and ISO 8601 calendar math.
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Lifestyle
Age Calculator
Free age calculator. Get your exact age in years, months, and days from any date of birth, plus total days lived, hours lived, weeks lived, and days until your next birthday.
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Lifestyle
Unit Converter
Free unit converter using exact NIST conversion factors. Convert between metric and US customary units for length, weight, temperature, volume, area, and speed.
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Real Estate
Square Feet to Square Meter Converter
Free square feet to square meter converter. Exact NIST factor: 1 sqft = 0.09290304 m². Bidirectional. Useful for international real estate, architecture, and design.
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Developer Tools
Unix Timestamp Converter
Free Unix timestamp converter. Translate Unix epoch seconds (or milliseconds) to ISO 8601, RFC 3339, and human-readable dates in any IANA timezone — and back.
Showing 61–72 of 178