Date Calculator: Add/Subtract Days, Weeks & Months
date ± unitsAdd days to date exclude weekends, subtract days from date calculator, calculate deadline date work days. Perfect for US tax deadlines, contract periods, and project scheduling.
US Exclusive Use Cases
This date calculator is tuned for American fiscal, employment, and academic date math:
- Add days to date exclude weekends: Add business days to any date, skipping weekends and holidays
- Subtract days from date calculator: Subtract days for deadline planning and countdown
- Deadline date calculator work days: Calculate project deadline dates based on working days
- Tax deadline projection: Pushing an IRS filing date forward or pulling an extension deadline back
- Probation period end: Finding when a 90-day US employee probation expires
- Contract term add/subtract: Adjusting contract start or end dates by months or years
- Project timeline days calculator: Build project schedules with accurate date calculations
US vs Global Calculation Differences
US date arithmetic prioritizes fiscal and employment cycles differently from other regions:
- Fiscal alignment: US month and year math aligns to IRS and corporate fiscal periods
- Employment-cycle aware: 90-day probation and annual review math follows US at-will employment norms
- Leap-year and month-length rules: Strict Gregorian handling matches US legal date computation
- No business-day auto-shift: US calendar arithmetic lands on the exact calendar date
Common Calculation Mistakes
Common mistakes: ignoring variable month lengths when adding months (January 31 + 1 month is not March 3), mishandling leap-year February when adding days, not distinguishing workday from calendar-day addition, and forgetting that a tax-period push may cross a holiday without auto-shifting. Use the correct unit (days vs business days) for your scenario.
Tool Algorithm & Precision Explanation
The calculator supports four units of arithmetic and multiple scenario modes:
- Units: add or subtract days, weeks, months, or years independently
- Add days to date: easily add any number of days, weeks, months, or years
- Subtract days from date: subtract days for deadline and countdown calculations
- Month-end safety: adding months to a month-end date clamps to the target month's last day
- Leap-year aware: correctly handles February 29 in leap years
US Federal Holiday & Workday Reference
When using business-day arithmetic, these federal holidays are skipped:
| Holiday | Date Rule | Arithmetic Impact |
|---|---|---|
| New Year's Day | January 1 | Shifts Q1 start dates |
| MLK Jr. Day | 3rd Monday in January | Mid-January skip |
| Presidents' Day | 3rd Monday in February | Feb deadline shift |
| Memorial Day | Last Monday in May | May 30/31 deadlines |
| Juneteenth | June 19 | Mid-year shift |
| Independence Day | July 4 | Early July skip |
| Labor Day | 1st Monday in September | Sept start shift |
| Columbus Day | 2nd Monday in October | Oct midpoint |
| Veterans Day | November 11 | Nov deadline |
| Thanksgiving | 4th Thursday in November | Nov shutdown |
| Christmas Day | December 25 | Year-end shift |
Project Management Mode — US Construction & Tech Schedule Rules
Project Management Mode applies US internet, construction, and outsourcing schedule standards by stripping legal shutdown days that generic calculators miss:
- Shutdown-day stripping: removes weekends + federal holidays + common US project shutdown days (Black Friday, Christmas Eve, New Year's Eve) when sites and dev teams go dark
- Forward deadline: from a kickoff date, walks forward N working days to land the correct delivery date
- Reverse back-calc: from a contract due date, walks backward N working days to find the latest safe start
- Delay accounting: a holiday inside the window extends the calendar span needed, so slippage shows up early
- Industry norm: US construction and tech contracts count only working days, never calendar days, for delivery milestones
PTO Vacation Mode — US Paid Leave Accrual Rules
PTO Vacation Mode follows US paid-time-off accounting, separating charged PTO days from free rest days that overlap a leave span:
- Charged PTO days: only business days (Mon-Fri minus federal holidays) inside the leave span consume an employee's PTO balance
- Overlapping weekends: Saturdays and Sundays inside the span are free — they do not deduct from PTO
- Overlapping holidays: a federal holiday inside the span is paid by the employer, not charged to PTO
- Overlap deduction rule: a vacation spanning a holiday weekend charges fewer PTO days than its calendar length suggests
- Enterprise norm: US HR systems prorate PTO this way; charging raw calendar days is a common payroll error
Frequently Asked Questions
How do I add days to a date excluding weekends?
Enter your start date, choose Add, enter the number of days, and select Days. For business days only, use the business days calculator instead.
How do I subtract days from a date for deadline calculations?
Enter your target date, choose Subtract, enter the number of days, and select Days. The result is your start date for the deadline.
How do I calculate a deadline date based on work days?
Use the date calculator to add working days to a start date, or subtract working days from a deadline date. The business days mode excludes weekends and federal holidays.
How is a 90-day US probation end date calculated?
Enter the hire date, choose Add, enter 90, and select Days. The result is the exact probation-end calendar date.
What happens when adding a month to January 31?
The calculator clamps to the target month's last valid day. January 31 + 1 month yields February 28 (or 29 in a leap year).
Can I subtract years from a contract start date?
Yes. Choose Subtract, enter the number of years, and the result moves the date backward by that many calendar years.
Is leap-year February handled correctly?
Yes. The engine uses strict Gregorian rules, so adding days across February 29 in a leap year is exact.