Date & Time
Age, duration & timezone calculators
Date Difference Calculator
Days, weeks and a calendar year/month/day breakdown between two dates, plus a business/working-days mode (weekdays minus US federal holidays with observed-date rules) and an inclusive/exclusive endpoint toggle. DST-safe UTC math, computed entirely in your browser. Accurate, instant and free — for United States.
What these mean:
What these mean:
From 2026-01-01 to 2026-01-31 is 30 days (0y 0m 30d) counted exclusive of the end date, or 31 days counting both endpoints. That is 20 business days (weekdays minus US federal holidays). Calendar math runs on UTC dates (DST-safe).
Total days
30
Weeks
4
Business days
20
Calendar breakdown
0y 0m 30d
30 total days · 31 counting both endpoints
Inclusive vs exclusive — the #1 off-by-one
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Calendar math is computed on UTC dates (DST-safe); business days use the US federal-holiday calendar with observed-date rules. Reference: ISO-8601.
ISO-8601 · US federal holidays
Take it further: shift a date forward or back with the Date Add / Subtract Calculator, or find the ISO week with the Week Number Calculator.
Days, weeks, months and years between two dates
The difference between two dates is the number of whole calendar days from the start to the end. This tool reports the total days, the count in weeks, and a calendar year / month / day breakdown — plus an optional business-days mode and an inclusive/exclusive endpoint toggle.
Total days & weeks
calendar days ÷ 7
days = ⌊(end − start) / 86,400,000 ms⌋ · weeks = ⌊days / 7⌋
Computed on UTC midnights so a day is always a full calendar day (DST-safe).
Months & years
calendar-aware borrow
largest whole months ≤ span, then residual days
Month-length aware (like an age calculation) — not a divide-by-30 approximation.
- 1Total days (exclusive): 31 − 1 = 30 days between the dates (nights).
- 2Inclusive of both endpoints: 30 + 1 = 31 days touched.
- 3Business days: 22 weekdays (Mon–Fri) minus New Year’s Day and MLK Day = 20 US working days.
Business / working days — weekends and observed holidays
Business (working) days are the weekdays — Monday to Friday — in the range, minus public holidays. The tool counts every weekday from the start date through the end date inclusive, then subtracts US federal holidays. A holiday that lands on a weekend is observed on the nearest weekday: Saturday rolls back to Friday, Sunday rolls forward to Monday.
Worked example · January 2026 working days
Inclusive vs exclusive endpoints
Counting exclusive of the end date gives the number of nights between the dates (Jan 1 → Jan 31 = 30). Counting inclusive of both endpoints gives the number of days touched (31). The one-day gap between these two conventions is the single most common off-by-one error, so the tool exposes an explicit toggle and labels each figure.
Pick the convention your deadline uses
DST-safe calendar math on UTC dates
Every calculation runs on UTC midnights, so a day is always a full calendar day — even across a daylight-saving transition where a local day is 23 or 25 hours long. Doing date math in local time across a DST boundary is a classic source of off-by-one errors; anchoring to UTC avoids it entirely.
Everything runs in your browser
Frequently asked questions
Subtract the start date from the end date. Counting exclusive of the end date, 1 January 2026 to 31 January 2026 is 30 days; counting inclusive of both endpoints it is 31 days. This calculator shows both, plus the difference in weeks and a calendar year/month/day breakdown, so you can read off whichever count your deadline uses.
Exclusive counting gives the number of nights between the two dates — it excludes the end day, so Jan 1 to Jan 31 is 30. Inclusive counting includes both the start and end days, giving the number of days touched, so Jan 1 to Jan 31 is 31. This one-day gap is the single most common off-by-one error, which is why the tool exposes an explicit toggle and labels each figure.
Business (working) days are the weekdays — Monday to Friday — in the range, minus public holidays. This tool counts every Mon–Fri from the start date through the end date inclusive, then subtracts US federal holidays. From 1 January 2026 to 31 January 2026 there are 22 weekdays; removing the two weekday federal holidays in that range — New Year’s Day (Jan 1) and Martin Luther King Jr. Day (Jan 19) — leaves 20 business days.
US federal holidays that land on a weekend are observed on the nearest weekday: a Saturday holiday is observed on the preceding Friday, and a Sunday holiday on the following Monday. The business-days count uses these observed dates, matching how offices and banks actually close.
Months and years use calendar-aware borrowing, the same logic as an age calculation — not a crude division by 30 or 365. The tool takes the largest whole number of months that does not overshoot the end date, then counts the residual days, so a span like 31 Jan to 1 Mar reads as 1 month 1 day rather than a rounded figure.
No. All calculations run on UTC midnights, so a day is always a full calendar day regardless of a 23-hour or 25-hour clock change during a daylight-saving transition. This prevents the off-by-one miscounts that arise when date math is done in local time across a DST boundary.
The result is order-normalized to an absolute value: the tool swaps the dates internally and always reports a positive count, so you never get a negative number of days. The difference between the two dates is the same either way.
Method & references
Methodology: total days = floor((end − start) / 86,400,000 ms) on UTC midnights; weeks = floor(days / 7); months/years use calendar-aware borrowing (largest whole months that do not overshoot, then residual days); business days = weekdays (Mon–Fri) in the inclusive range minus US federal holidays with observed-date rules (Sat → Fri, Sun → Mon). All calculations run client-side and nothing is stored.
Cross-links
How we calculate this
Reviewed by Reckonist Editorial · Last reviewed July 2026. Figures follow the methods and sources set out in our editorial standards.
Calendar math is computed on UTC dates (DST-safe); business days use the US federal-holiday calendar with observed-date rules. Reference: ISO-8601.
Keep going
Same-category tools follow this colour; a cross-category link keeps its own.