Everyday

Convert your dog or cat's age into the rough "human-year equivalent" — using vet-recommended scales, not the old multiply-by-seven myth.

Pick a coffee / tea / cola dose and see how much caffeine is still in your bloodstream now, in an hour, in six — and when it'll drop below the sleep threshold.

Convert between cups, tablespoons, teaspoons, millilitres, and fluid ounces — and weigh common ingredients in grams or ounces.

Compute Body Surface Area in m² using five published formulas — Mosteller, Du Bois, Haycock, Boyd, Gehan & George — side by side.

Convert between hourly, weekly, monthly, and yearly pay — with configurable work week and paid holidays.

Evaluate arithmetic expressions with the usual math functions — `sqrt`, `sin`, `log`, `pow`, `min/max`, and constants `pi`, `e`, `tau`.

Format a number the way each locale expects — `1,234,567.89`, `1.234.567,89`, `$1.23M`, `12 345 ₽` — and grab the matching JavaScript snippet.

Add tax to a net price or extract tax from a tax-inclusive price. Common VAT/GST/sales tax presets (5–25%).

Sum daily start/end times into a weekly total, subtract breaks, and split regular vs overtime. Optional hourly rate computes the paycheck.

Compute running pace, finish time, or distance from any two of them. Presets for 5K, 10K, half, and marathon.

Show day of year, ISO 8601 week, quarter, Julian day, Unix timestamp, leap-year status, and year progress for any date.

Estimate password strength via entropy and crack-time. Detects common passwords, sequences, and repeated characters. Nothing leaves your browser.

Factor an integer into primes, list all divisors, and compute GCD and LCM of two numbers. Handles values up to ~10¹².

Validate ISBN-10 and ISBN-13 checksums and convert between the two formats. Hyphens and spaces are handled.

Estimate daily water needs from weight, activity, climate, and pregnancy/breastfeeding status — gives a target and a 4-block schedule.

Compute your weighted GPA across courses on US 4.0, US 4.3 (+ grades), or Korean 4.5 scales. Tracks total credits and quality points.

Pour-over, French press, AeroPress, espresso, cold brew — calculate coffee and water amounts from any ratio with method-specific defaults.

Validate a card number with the Luhn checksum, detect brand (Visa/MC/Amex/etc), and check expected length. Local, no network.

Validate an International Bank Account Number — checks country code, length, and the mod-97 checksum. Supports 75+ countries.

Split your daily calories into grams of protein, carbs, and fat — IIFYM-style presets for balanced, low-carb, high-protein, or keto.

Compute your 5 training zones from age and resting HR — pick max-HR formula (Tanaka / Fox / Gulati) and method (%MHR or %HRR / Karvonen).

Estimate body fat percentage from height, neck, waist (and hip for women) using the US Navy tape-measure formula.

Estimate your due date from LMP, conception date, or ultrasound — see current weeks and trimester.

Calculate the sale price after a percent or fixed discount — plus tax, savings, and effective discount rate.

Find the best bedtime or wake time aligned to 90-minute sleep cycles so you wake up between cycles, not mid-deep-sleep.

Estimate your basal metabolic rate, daily calorie needs, and cut/maintain/bulk targets — Mifflin-St Jeor formula.

A click counter that survives a refresh — multi-counter, custom step, goal alert, and keyboard shortcuts.

Distraction-free scratch pad that autosaves to your browser — no account, no upload, no ads.

Calculate the monthly payment, total interest, and full amortization schedule for any fixed-rate loan.

Project how a starting balance grows with regular contributions, your interest rate, and your compounding frequency.

Calculate exact age in years, months, days — and find your next birthday.

Calculate Body Mass Index from height and weight, with a healthy range.

Calculate the tip and split the total bill between people.

Work out percentages, what-percent, and percent change in one place.