Date & Time Calculators

Count the exact number of days between any two dates — all calendar days, weekdays only, or business days (skipping US federal holidays). Pick whether to include both endpoints or just the difference.

Calculate the number of weeks between two dates as a decimal, plus a whole-weeks-and-days breakdown.

Add or subtract two time values in HH:MM:SS form. Returns the result as HH:MM:SS, total decimal hours, and total seconds. Handles values longer than 24 hours.

Count whole calendar months between two dates, with the leftover days reported separately.

Compute years between two dates with a years/months/days breakdown — useful for tenure, anniversaries, and exact-age questions.

Calculate age down to the second — years, months, days, hours, minutes, and seconds. Useful for milestones and trivia.

Add days, weeks, months, or years to any date and get the resulting date — handles month-end clamping correctly.

Subtract days, weeks, months, or years from a date — for things like "what date was 90 days ago?" or "5 years before today".

Convert any date into its ISO 8601 week number, US week number, and day of the year.

What day of the week was (or will be) any given date? Useful for historical curiosities and scheduling.

Is a given year a leap year? Apply the Gregorian rule with a step-by-step explanation.

Compute gestational age (weeks + days) from last menstrual period. Not medical advice.

Predicted ovulation date and fertile window from LMP and cycle length. Not medical advice.

Pregnancy week, trimester, and weeks-until-due from LMP. Not medical advice.

Predict the next 6 expected period start dates from a recent period and cycle length. Not medical advice.

Estimated due date = conception + 266 days. Not medical advice.

Estimated conception window = due date − 266 days, ± a few days for fertile window. Not medical advice.

Compute your retirement date from date of birth and target retirement age.

Years celebrated, days to next, and traditional/modern gift suggestions.

List US federal holidays for any year (2024-2030 hardcoded) with day-of-week.

Convert a date+time from one IANA time zone to another.

Count business days (Mon-Fri, excluding US federal holidays) between two dates.

Total work hours = business days × hours/day, optionally including weekends.

Compute hours and minutes between two HH:MM times, handling overnight wrap.

Convert any number of minutes to hours, hours-and-minutes, and decimal hours.

Hours worked = clock-out − clock-in − break minutes.

List the next 6 payday dates given period type and an anchor date.

Enter daily hours; calculator splits into regular (≤40) and OT (>40).

Suggested bedtimes from a wake time, or suggested wake times from a bedtime — both built on 90-minute sleep cycles + a fall-asleep buffer.

Days, hours, minutes, seconds remaining until a target date.

Days, hours, minutes, seconds elapsed since a past date.

Add up clock-in / clock-out times across a 7-day week, subtract breaks, output decimal or HH:MM.

Project hours → number of pomodoros, total clock time, long-break count — Pomodoro Technique by Francesco Cirillo.

Word count + reading speed → minutes / hours. Speed presets calibrated to research averages.

Time = horizontal distance ÷ 5 km/h + 1 hr per 600 m ascent. With Tranter's fitness corrections.

Weekly sleep debt = (target × 7) − actual hours slept. With recovery estimate and chronic-debt category.

Apply published time corrections from a NOAA primary tide station to estimate high/low tide times at a secondary station.

Solar position algorithm — equinox-day-of-year + latitude → sunrise + sunset + solar noon. Within ±2 min of NOAA Sun Calculator for ±60° lat.

Phase + illuminated fraction + age of moon for any date. Synodic-cycle approximation from a known new moon reference (Jan 6, 2000).

Break the gap between any two dates into a Y/M/D triple using the standard borrow-forward rule, plus the total in days, weeks, and months for cross-checking.

Subtract one time from another and read the result as HH:MM:SS plus total seconds, minutes, and decimal hours. Handles cross-midnight spans automatically.

Pick a meeting time in one time zone and see what it looks like everywhere else. DST-aware via Intl.DateTimeFormat. Workday-hours flagged per zone.

Add up worked hours from multiple clock-in/clock-out entries with break deductions, and see total and overtime hours.

Find the date of Easter Sunday for any year, using the Gregorian (Western) or Julian (Orthodox) computus.