Total Days
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Date Calculator & Day Counter
Date addition/subtraction, period breakdown, and countdown in one place
Local Processing Only
Add/Subtract Dates
Calculate dates by days, weeks, months, or years.
Result
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Enter a base date and amount
Analyze Difference Between Two Dates
See total days, week equivalents, Y/M/D breakdown, and weekday/weekend split.
Week Equivalent
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Y/M/D Breakdown
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Weekdays / Weekends
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Countdown to Target Date
Check remaining or elapsed days between today and your target date.
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Enter a target date
How to Use
Set base date, amount, and unit in add/subtract mode.
Use presets for common windows such as +30 days or +3 months.
Analyze total days, week equivalents, and Y/M/D breakdown between two dates.
Use countdown output to back-plan deadlines and event schedules.
FAQ
How are month/year additions handled?
When the target day does not exist, the result is clamped to the last valid day of that month.
What does 'include end date' mean?
It adds the end day itself as one extra counted day.
Are holidays included in weekday/weekend split?
No. The split is based only on weekday names, not public holiday calendars.
Does countdown depend on time zones?
It uses local calendar days in your browser, not time-of-day precision.
Are my dates uploaded?
No. Calculations run locally in your browser.
Does changing the reference date change the result?
Yes. Age and day-difference results depend on the reference date. When comparing, keep the reference date the same.
Why does it say “invalid date”?
Dates that don’t exist (e.g., Feb 30, or Feb 29 on a non-leap year) will fail validation. Review your input and try again.
How are era change boundary dates handled?
The era changes on the official change date. For formal documents around boundaries, do a quick manual check of the output.
References
- MDN: Date
Core browser API behavior for date math.
- IANA Time Zone Database
Foundational timezone reference data.
- NAOJ Calendar Calculations
Official Japanese calendar calculation references.
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