Date math looks trivial until you hit the traps: full age vs traditional age differing by one or two years, forgotten weekends in a schedule, a due date that never matches the ultrasound. Tools handle all of it instantly.
Age: Full Years, Traditional Years and Birthdays
Full age (zhou) counts completed years — the legal standard on forms. Traditional age (xu) starts at 1 and increments at New Year, landing 1-2 above. Enter a birth date and get exact years-months-days, total days lived, and days to the next birthday — useful for milestone birthdays and tracking baby age against vaccine schedules.
Pregnancy: Due Dates and Fertile Windows
- Naegele's rule: first day of last period + 280 days (40 weeks); the tool also shows current gestational week.
- A due date is an estimate — birth between weeks 37-42 is normal, two weeks either way is common.
- Ovulation ≈ 14 days before the next period, with a fertile window of about 10 days — accurate only when based on your own cycle length.
Schedules: Don't Let Weekends Trick You
How many working days is 'two months to deliver'? Enter both dates and get total days, working days and weekend counts — handy for contract durations, leave requests and payroll cycles. For exams, weddings and launches, a date countdown shows the remaining days at a glance.
Recommended Tools
Age Calculator
Find your exact age in years, months and days, plus a countdown to your next birthday.
Due Date Calculator
Enter the first day of your last period to estimate your due date and current pregnancy week.
Date Countdown
Count the days to an exam, wedding or holiday with a live days-hours-minutes timer.
Business Days Calculator
Count total days, weekdays and weekend days between two dates.
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FAQ
Do working-day calculators include public holidays?
Generic tools count Monday-Friday only. For holiday-sensitive schedules (construction timelines), subtract statutory holidays manually from the result.
Why does the ultrasound differ from the calculated due date?
Early-pregnancy ultrasound measures fetal development directly and is considered more accurate; doctors adjust the due date accordingly. The formula is only the first estimate.