Days Between Dates Calculator

How the Days Between Dates Calculator Works

The calculator subtracts the start date from the end date to get the number of days. It then converts that number into weeks, months, and years for additional context. For business days, it counts only Monday through Friday, excluding weekends.

Note: This business day calculator does not exclude federal holidays — if you need to exclude holidays (e.g., for legal deadlines or contract terms), add the number of holidays in the range to your count.

Common Uses for Date Difference Calculation

• Contract and legal deadlines: Calculating response windows, notice periods, and filing deadlines — often specified in "business days" or "calendar days"
• Pregnancy tracking: Calculating weeks of pregnancy from last menstrual period or conception date
• Event planning: How many days until a wedding, vacation, or product launch
• Age in days: How old am I today in days? (use your birthday as start date and today as end)
• Project timelines: How many business days between kickoff and deadline?
• Loan and lease terms: Exact day count for interest calculations or lease end dates
• Historical research: How many days between two historical events?

Calendar Days vs. Business Days

The distinction between calendar days and business days matters significantly for legal, financial, and professional deadlines:

• Calendar days: Every day counts — including weekends and holidays. Used in most informal contexts and many legal contexts (e.g., "the 30-day return window")
• Business days: Only Monday through Friday count. A "5 business day" shipping window that starts on Thursday means delivery the following Wednesday, not the following Tuesday. Commonly used in banking, legal filings, and employment notices
• Read contracts carefully: "Days" usually means calendar days unless explicitly stated otherwise. "Business days" or "working days" means weekdays only

How Months Are Counted

Counting months between dates is more complex than it appears because months have different lengths (28, 29, 30, or 31 days). There are two common approaches:

• Calendar month counting: January 15 to March 15 = 2 months. January 31 to March 31 = 2 months. This is the approach used in most contracts and everyday usage
• 30-day month approximation: Simply divide total days by 30. January 1 to March 1 = 59 days ÷ 30 = 1.97 months. Less precise but sometimes used in financial calculations

This calculator shows both months and weeks, giving you multiple ways to express the same duration.

Interesting Date Differences

• New Year's Day to July 4th: 184 days (non-leap year)
• July 4th to Christmas: 174 days
• A standard school year (Sep 1 – May 31): 272 calendar days / ~195 school days
• A standard work year: 260 business days (52 weeks × 5 days)
• A 30-year mortgage: 10,957–10,958 calendar days (depending on leap years)
• 1 million seconds: 11.57 days
• 1 billion seconds: 31.7 years

Frequently Asked Questions

How many days are in a year? 365 in a non-leap year, 366 in a leap year. Leap years occur every 4 years (divisible by 4), except century years not divisible by 400 (2000 was a leap year; 1900 was not).

Is today included in the count? This calculator counts from the start date up to (but not including) the end date. So January 1 to January 2 = 1 day. If you want to include both the start and end date in your count, add 1 to the result.

How do I calculate a date X days from today? Enter today as the start date and leave the end date empty — or use the age calculator for birthday-based math. For "what date is 90 days from today," you'd need an add-days calculator.

What are the most common business day windows? 3 business days (standard check clearing), 5 business days (1 week), 10 business days (2 weeks), 30 business days (~6 weeks), 45 business days (~9 weeks).