Calculate days between dates, add or subtract days, find date differences, and plan future events.
Common Date Calculations
Business Day Calculations
When calculating deadlines, contracts, or payment terms, business days (excluding weekends and holidays) matter. Typical: 5 business days ≈ 7 calendar days, 10 business days ≈ 14 calendar days, 30 business days ≈ 6 weeks.
Pregnancy Due Date
Pregnancy lasts approximately 280 days (40 weeks) from last menstrual period (LMP). Add 280 days to LMP to estimate due date. Only 5% of babies arrive on exact due date—normal range is 37-42 weeks.
Age Calculation
Calculate exact age by finding date difference from birth date to today. Includes leap years and varying month lengths automatically. Legal age for various purposes: voting/smoking/military (18), drinking in US (21), Medicare eligibility (65), full retirement age (66-67).
Anniversary and Event Planning
Calculate days until important events: weddings (plan 12-18 months ahead = 365-545 days), milestone birthdays, vacations, project deadlines, contract expirations. Knowing exact days helps with countdown planning and milestone tracking.
Frequently Asked Questions
How do I calculate days between two dates?
Subtract earlier date from later date. Our calculator handles this automatically including leap years and varying month lengths. Example: From January 15, 2025 to March 20, 2025 = 64 days. Manual: (31-15) Jan + 28 Feb + 20 Mar = 16+28+20 = 64 days. Calculator accounts for leap years (366 days vs 365) automatically.
How many days in each month?
January: 31, February: 28 (29 leap years), March: 31, April: 30, May: 31, June: 30, July: 31, August: 31, September: 30, October: 31, November: 30, December: 31. Mnemonic: "30 days has September, April, June, and November. All the rest have 31, except February alone." Leap years occur every 4 years (divisible by 4), except centuries (divisible by 100) unless also divisible by 400. So 2000 was leap year, 1900 wasn't, 2024 is, 2100 won't be.
What is a business day?
Business days are Monday-Friday, excluding public holidays. Used for: contract deadlines, payment processing, shipping estimates, legal timelines. Calculating: 1 week = 5 business days, 1 month ≈ 20-23 business days (depending on weekends/holidays), 1 year ≈ 250-260 business days. Note: business days vary by country—some nations include Saturday or have different holiday calendars.
