Month-end and leap years
The browser’s calendar rules handle uneven months and Feb 29, so add/subtract and span math stay consistent with real dates instead of flat 30-day blocks.
Add, subtract, count workdays
Date Calculator: Add or Subtract Days from a Date, or Count Days Between
Roll a date forward or backward by days, weeks, months, or years, or measure the gap between two fixed dates. In Difference mode you can strip weekends and pick a US, UK, or Canada holiday list for a working-day total. Inputs stay in your browser.
By Jeff Beem
Updated
01
Mode
Operation
Result
Sunday, July 12, 2026
Totals
Months0 Months
Weeks0 Weeks
Days0
Hours0 Hours
Minutes0 Minutes
Seconds0
02
How it works
Why manual counts go wrong
Off-by-one skips, different weekend rules, and observed holidays on substitute weekdays are the usual reasons paper counts disagree with a machine count.
Business-day counts
Weekend and holiday exclusions apply only in Difference mode and change the working-day total, not the calendar span breakdown.
Switch to Difference to configure exclusions.
US federal holidays
Observed dates (Friday or Monday substitutes) are what the list removes, often where hand counts drift.
UK bank holidays
England & Wales observed bank holidays, including substitute weekdays when the statutory day falls on a weekend.
DST
This tool counts calendar dates, not clock-hour spans across DST. Use a time calculator for exact clock deltas.
Reading the span
Add / subtract lands on a future or past date from one anchor. Difference measures between two fixed endpoints. Most mix-ups come from using Difference when you needed to roll forward 90 days, or from comparing a calendar-day total to HR’s business-day rule.
Example: +90 days from March 1, 2026
In Add / subtract, set the base date to March 1, 2026, enter 90 in the days field, leave years/months/weeks at zero, and tap Add. The panel shows Saturday, May 30, 2026, with the span broken into months, weeks, and total days. That is the pattern for “90 days from signing” clauses when the contract names a start date instead of today.
Business days live in Difference mode
Weekend and holiday toggles only apply when both endpoints are fixed. Flip to Difference, set start and end, then exclude weekends or pick US federal, UK England & Wales, or Canada federal holidays. The yellow business-day line is inclusive of both boundary dates unless your policy says otherwise; confirm against your paperwork before you email HR.
Months are not 30-day blocks
Adding one month to January 31 does not mean “add 30.” The tool uses browser calendar rules, so you may land in February on the 28th or 29th. Leases that say “calendar month” still need a sanity check against the output, not mental arithmetic.
Date Calculator: Add, subtract, and compare dates
Contract notices, payroll windows, and launch countdowns all need the same question answered twice: which calendar day, and how many workdays count inside the span.
What this calculator does
In Add / subtract, start from one calendar day and roll forward or back by years, months, weeks, or days until you reach the landing date you need (notices, renewals, “60 days from signing,” and similar). In Difference, fix two endpoints and measure how far apart they are in calendar time. Turn on optional weekend stripping and holiday stripping (US federal, UK England and Wales bank holidays, or Canada federal) when the question is really “how many business days” inside that span. You get weekday names, span breakdowns, and working-day totals when exclusions apply. It does not replace clock arithmetic across time zones or shift schedules; for hours and minutes on the same day, use a time calculator. For age-style wording between birthdays, use an age calculator. When you start from two birth dates and want the gap between people rather than one lifespan, use the Age Difference Calculator. Everything runs locally in your browser.
Spreadsheets lie kindly. They’ll add 30 to a date cell and call it a month when your contract means “calendar month.” Business-day counts need a chosen exclusion list, and the right list depends on whose office calendar you’re using. This page keeps those toggles in plain sight so the argument happens once, in writing, not every quarter when someone reruns the numbers in their head.
Worked examples
90 days from a contract date: Add / subtract mode, base March 1, 2026, days = 90, Add → Saturday, May 30, 2026. 60 or 180 days: same mode; enter the offset, Add or Subtract for direction. Gap between two dates: Difference mode with start and end; read total calendar days (enable exclusions for working days). Biweekly: treat “every two weeks” as adding 14 calendar days from each result when you need the next occurrence. If someone means twice per calendar week, clarify before you stake a deadline on it.
How the Math Works
Whole-day gaps boil down to milliseconds between midnight anchors, then floor-divided by the length of a solar day in milliseconds. In symbols: Calendars are messy. Months aren’t equal. February steals or adds a day. When you add “one month” inside the tool, the stepping follows the same calendar rules your browser uses for Date objects, which is why January 31 plus one month doesn’t pretend February has 30 days.
Business-day counts start from the calendar span you asked for, then drop weekend dates and any holiday dates that fall inside the selected region’s list. Think of it as subtracting rows from a printed calendar when those rows are Saturdays, Sundays, or marked holidays. Weekend skipping uses weekday arithmetic instead of walking day by day, which keeps large ranges fast. Holiday hits come from a precomputed set for the region you picked.
DST doesn’t change the integer day index unless you cross midnight on the civil calendar; we’re not measuring 23-hour or 25-hour clock days here. If you need that precision, you’ve left “date math” and entered “timestamp math.”
Tiny example
Picture 14 calendar days between a Monday start and a Monday two weeks later. Raw count: 14. Throw out weekends inside that window and the working-day number drops. Throw out a federal Monday holiday and it drops again. Same two anchors, three different answers depending on the question. The UI keeps those stories separate so you don’t merge them by accident.
Why your business-day count doesn’t match the wall calendar
People love arguing this one. Usually they counted weekends twice, forgot whether the delivery date itself counts, or used a holiday list from the wrong country. Observed holidays make it worse: when Christmas lands on Saturday, many offices take the Friday or Monday instead. This calculator uses its built-in tables for the region you pick, not your paper desk calendar from five years ago. If your employer uses a custom list, treat the built-in total as a baseline and adjust manually. Still beats counting rows with a highlighter.
Another trap: mixing “how many weekdays between” with “how many business days until.” One cares about interior weekdays only; the other often cares whether the deadline day itself is workable. Different nouns, different math. Say which story you need before you paste dates into email. Your colleagues will act like this distinction is obvious. It is not.
End-of-month surprises when you add months or years
Month math punishes optimism. Add a month to the 30th of a short month and you might land earlier than you pictured. Add years across a leap day and February reminds you it exists. The tool mirrors JavaScript calendar stepping so it matches what most web apps do, which is what you want when you sanity-check software dates. If your lease uses literal “calendar months,” confirm against the output instead of mentally adding 30 days.
Holiday regions: what each option really means
US federal focuses on federal observances in the common list people mean when they say “bank holiday” in the US. UK England and Wales follows bank holidays for that jurisdiction, not Scotland’s separate list. Canada federal tracks federal statutory holidays nationwide; provinces can differ. Pick the closest match. None of these replace legal advice for filing deadlines; they replace guesswork for everyday scheduling.
Date Calculator FAQ
How do I add days to a date?
Choose Add / subtract, set your start date, enter the number of days in the days field (and months or years if needed), then tap Add. The result shows the new calendar date and weekday.
How do I subtract days from a date?
Stay in Add / subtract. Enter the same offsets, then tap Subtract instead of Add. That rolls the calendar backward by the amounts you typed.
How many days are between two dates?
Switch to Difference. Put the earlier date in start and the later date in end. The tool shows total calendar days plus a years/months/days breakdown. Turn on weekend or holiday exclusions only if you want a working-day style count rather than raw calendar days.
How do I calculate 60 days from a date (or 180 days)?
Use Add / subtract. Pick the anchor date, type 60 or 180 in the days box, leave other offsets at zero unless your rule uses months, then tap Add. For “180 days before,” use the same offset with Subtract.
How do biweekly (every two weeks) dates work?
Biweekly usually means “every 14 calendar days.” In Add / subtract, add 14 days repeatedly from each landing date to step forward. If your policy uses business weeks instead, confirm whether weekends count with whoever owns the rule.
Why is my business-day count different from my manual count?
Hand counts skip rules. Three things bite people: counting the start or end day differently, forgetting weekends, and forgetting that holidays sometimes move when they fall on a Saturday. This tool applies one consistent rule set so you can argue with the spreadsheet, not with yourself.
How do I calculate 90 days from today?
Stay on Add / subtract. Leave the base date as today unless the contract names another anchor. Put 90 in the days box. Hit Add. Done.
How do I count business days between two dates?
Switch to Difference. Enter start and end. Turn on weekend exclusion if Saturdays and Sundays should not count. Add holiday exclusion if US federal, UK bank, or Canada federal calendars match your office. The working-day line is the one HR usually cares about.
What happens if the end date lands on a weekend or holiday?
Calendar math doesn’t magically erase a weekend on the calendar. The span in plain days stays what it is. Flip on exclusions only if you’re asking how many workdays fall inside the range. Different question, different number.
Does daylight saving time affect the date count?
No for day-based answers. We stay on calendar dates in your local zone, so spring-ahead doesn’t shrink the count by a day. Need hour-by-hour deltas across a DST jump? Use a time-duration tool instead.
What happens when I add one month to a date near the end of the month?
Months are uneven. The code follows normal JavaScript calendar stepping, same as most browsers. That means January 31 plus one month lands in February according to those rules instead of pretending every month has 30 days.
Which holiday calendars can I exclude?
US federal, UK England and Wales bank holidays, or Canada federal. Choose the set that matches real closures where you work. Provincial or state quirks may still need a manual tweak.
Time & Date Reference Note
Informational Use: These tools use standard date/time algorithms and your browser’s timezone data (IANA). Results are intended for general reference and planning only.
Verification Recommended: Time zone rules and daylight saving changes vary by region and year. For critical scheduling, payroll, or legal deadlines, confirm results with official sources.
Local Verification: Always confirm times, dates, and business-day counts with official sources or qualified professionals when stakes are high.
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