About HowManyDays.app
HowManyDays.app is a free, privacy-first collection of online date and time calculators. Simple date calculations — counting days between dates, calculating age, finding moon phases — should not require an account, a server round-trip, or exposing your personal data.
Our Mission
To provide fast, accurate, and completely private date and time calculation tools that work entirely in your browser. No data leaves your device. No tracking. No sign-ups.
Methodology
Every calculator runs client-side using JavaScript. All date/time math uses standard JavaScript Date objects. Moon phase calculations use an astronomical approximation accurate to within 1-2 days. Timezone conversions follow IANA timezone database rules via Intl.DateTimeFormat. No data is ever sent to our servers.
Our Calculators
- Days Between Dates — Exact count between any two dates
- Age from Birth Year — Age by year of birth
- Age in Days & Weeks — Age in smaller units
- Countdown Timer — Time remaining to a target date
- Workdays Counter — Working days (excl. weekends)
- Weeks Between Dates — Weekly interval calculator
- Hours & Minutes Difference — Time difference
- Timezone Converter — Convert across timezones
- Moon Phase Calculator — Lunar phase for any date
- Leap Year Checker — Check if a year is a leap year
- Day of the Week Finder — Day for any date
- Chinese Zodiac — Zodiac by birth year
- Days Until Date — Countdown to a date
Privacy
We do not collect, store, or share any personal data. See our Privacy Policy.