📅 Date Calculator
Calculate days between dates, add or subtract days, find business days, and plan events with precision.
Date Calculation Guide
Our date calculator helps you work with dates for planning events, calculating deadlines, tracking project timelines, and more.
Common Use Cases
- Event Planning: Calculate days until a wedding, birthday, or holiday
- Project Management: Determine deadline dates and milestone timing
- Legal & Business: Calculate notice periods, contract durations, payment terms
- Personal: Track anniversaries, count days in a relationship, pregnancy due dates
- Travel: Plan trip durations and return dates
📊 Business Days vs. Calendar Days
Calendar days include all days (weekdays + weekends). Business days typically exclude Saturdays and Sundays. For legal or financial deadlines, always clarify which type of days are meant.
Date Math Formulas
Days in Each Month
Remember with this rhyme: "30 days has September, April, June, and November. All the rest have 31, except February which has 28 (or 29 in leap years)."
Leap Year Rule
A year is a leap year if:
- It's divisible by 4
- BUT if divisible by 100, it must also be divisible by 400
- 2024, 2028, 2032 are leap years
- 2100, 2200, 2300 are NOT leap years (divisible by 100 but not 400)
- 2000, 2400 ARE leap years (divisible by 400)
Week Number Calculation
ISO week numbering: Week 1 is the week containing the first Thursday of the year. A year has 52 or 53 weeks.
Date Calculation Reference: Key Facts & Conversions
Quick reference data for common date calculations, business day counts, and time unit conversions:
Days Per Month & Quarter
| Month |
Days (regular) |
Days (leap year) |
Quarter |
Business Days (avg) |
| January | 31 | 31 | Q1 | 23 |
| February | 28 | 29 | 20 |
| March | 31 | 31 | 23 |
| April | 30 | 30 | 22 |
| May | 31 | 31 | 22 |
| June | 30 | 30 | 21 |
| July | 31 | 31 | 23 |
| August | 31 | 31 | 22 |
| September | 30 | 30 | 22 |
| October | 31 | 31 | 23 |
| November | 30 | 30 | 20 |
| December | 31 | 31 | 22 |
| Full Year | 365 | 366 | × | ~261 |
Leap Year Rule: A year is a leap year if: (1) it's divisible by 4 AND (2) if divisible by 100, it must also be divisible by 400. So 2000 was a leap year (×400), 1900 was NOT (×100 but not ×400), and 2024 IS (×4, not ×100). Next leap years: 2028, 2032, 2036, 2040, 2044, 2048.
? Frequently Asked Questions
How do I count days including start and end dates?
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By default, day counting is exclusive of the end date (e.g., Jan 1 to Jan 10 = 9 days). To include both dates, check the "Include end date" option, which adds 1 to the count. This is often needed for legal deadlines or vacation day counting.
What are business days?
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Business days (also called working days or weekdays) typically exclude Saturdays and Sundays. In some contexts, they also exclude public holidays. Our calculator excludes weekends; for holidays, you may need to manually adjust the count based on your region.
How many business days are in a year?
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A typical year has 260-262 business days (52 weeks × 5 days), depending on which day the year starts and ends. After subtracting public holidays (typically 10-15 in the US), most workers have about 250 working days per year.
How do I calculate months between dates?
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Months are calculated by counting complete months between dates. Since months have different lengths (28-31 days), "1 month" isn't an exact number of days. For precise calculations, our tool shows both the approximate months and exact days.
What is the ISO week number?
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ISO 8601 defines week 1 as the week containing the first Thursday of January. Weeks start on Monday. This means January 1 could be in week 52 or 53 of the previous year if it falls on Friday, Saturday, or Sunday.