To calculate days between two dates, you subtract the earlier date from the later date. In practice, dates are converted to a standard format (like Julian Day Numbers or Unix timestamps) to handle different month lengths and leap years. The basic formula is: Days = End_Date - Start_Date. For example, from January 1, 2025 to January 31, 2025 equals 30 days. Our calculator handles all the complexity automatically, including leap years, varying month lengths, and century adjustments!

Yes! All reputable date calculators (including ours) automatically account for leap years. A leap year occurs every 4 years, except for years divisible by 100 (unless they're also divisible by 400). So 2024 was a leap year, but 1900 wasn't, while 2000 was. This means February 29 is properly handled in all calculations. Without accounting for leap years, date calculations would be off by one day for every leap year in the date range!

Calendar days include every single day—weekends, holidays, everything. Business days (also called working days or weekdays) typically only count Monday through Friday, excluding weekends. Some business day calculators also exclude public holidays. For example, if a contract says "payment in 10 business days," that's 10 weekdays, which could span 14 calendar days if it includes two weekends. This distinction is super important in legal contracts, delivery schedules, and project planning!

Pregnancy due date calculators provide an estimate, not an exact date! They typically use Naegele's Rule, which assumes a 28-day menstrual cycle and adds 280 days (40 weeks) to the first day of your last menstrual period. However, only about 5% of babies actually arrive on their exact due date! Most babies are born within two weeks before or after the estimated due date. Factors like cycle length, conception date accuracy, and individual variations affect the actual delivery date. Your healthcare provider will use ultrasounds and other measurements to refine the estimate!

Absolutely! Date calculators work both ways—forward into the future and backward into the past. You can calculate how many days ago something happened, what date it was X days before a certain date, or how old something is. This is useful for historical research, legal backdating, calculating interest accrual periods, or just satisfying curiosity (like figuring out what day of the week you were born on!). Our calculators handle past dates just as accurately as future ones!

Blame the Romans! Our calendar evolved from the Roman calendar, which was a bit of a mess. Julius Caesar reformed it (creating the Julian calendar), and Pope Gregory XIII refined it further (creating the Gregorian calendar we use today). The varying month lengths (28-31 days) are historical artifacts from these reforms. The mnemonic "30 days hath September, April, June, and November; all the rest have 31, except February" helps remember which is which. February got the short end with only 28 days (29 in leap years) because it was originally the last month of the Roman year!

Use our Age Calculator! Just enter your birth date and the date you want to calculate your age on (usually today). The calculator will tell you your exact age in years, months, days, and even hours! For example, someone born on January 1, 2000, would be approximately 25 years, 9 months, and 25 days old on October 26, 2025—or about 9,429 days, or 226,296 hours! This is perfect for celebrating unique milestones like your 10,000-day birthday or your 1 billion-second anniversary!

Use the "Add Days to Date" calculator! Enter today's date (or any starting date) and add 90 days. The calculator will tell you the exact date, accounting for varying month lengths and leap years. For example, 90 days from October 26, 2025 would be January 24, 2026. This is super useful for calculating warranty expiration dates, project deadlines, subscription renewals, or planning events. You can add any number of days—10, 30, 100, 365, whatever you need!

Date calculators typically focus on calendar dates rather than specific times, so time zones don't usually matter for day-based calculations. When calculating days between January 1 and January 31, it's 30 days regardless of time zone. However, if you're calculating down to hours and minutes, time zones become important. Our basic date calculators work with calendar dates, which makes them universal—the same calculation works whether you're in New York, London, Tokyo, or Sydney. For time-specific calculations across time zones, you'd need a dedicated time zone converter!

Yes! Date calculators are essential in finance for calculating interest accrual periods, investment maturity dates, payment due dates, loan terms, and fiscal periods. Terms like "Net 30" (payment due 30 days after invoice date) require accurate date calculation. However, financial institutions often use specialized day count conventions (like 30/360 or Actual/365) that might differ from simple calendar day counting. For basic date calculations in contracts, invoicing, and scheduling, our calculators work perfectly. For complex financial instruments, consult financial professionals who can apply the specific conventions your situation requires!