Date math you can verify
One question. Multiple valid counting rules.
DYFRO calculates dates, compares interpretations, and explains exactly why two answers can differ.
1Choose the rule
2See the date
3Verify the receipt
Example · 2026-11-13 UTC
Compare your date →What does “90 days from today” mean?
RuleResultDifference
90 calendar daysThursday, February 11, 2027standard
InclusiveWednesday, February 10, 2027−1 day
90 weekdaysFriday, March 19, 2027weekends skipped
3 calendar monthsSaturday, February 13, 20272 day(s) vs 90d
Quick answers
Jump straight to a common interval
Open a live date with its counting receipt, then compare the rule before you rely on the result.
Signature tools
Built for cases ordinary calculators hide
01
Date Debugger
Enter the answer you expected and identify the likely counting rule.
02Rule comparison
Calendar, inclusive, weekday, business-day, and month arithmetic side by side.
03Deadline rule builder
Define the counting convention before trusting the date.
04Business-day math
Use your own non-working weekdays, optional federal preset, and closure dates.
05ISO week number
Find the ISO week-year and its Monday-to-Sunday range.
Why DYFRO
The answer without the rule is incomplete.
Inclusive counting, business-day calendars, month-end rules, and time zones can all change a result.
- Transparent start-day handling
- Month-end clamping explained
- Business-day assumptions shown
- Browser-local interactive result
- Calculation receipt
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