How to Calculate the Days Between Two Dates
How many days until your vacation? How many business days between signing a contract and the deadline? How many days has it been since a specific event? These are all "days between dates" problems, and they come up more often than you might think.
This guide covers manual counting methods, leap year rules, the difference between calendar days and business days, and real-world applications from project management to pregnancy tracking.
✨Key takeaways
- Calendar days: count every day, including weekends and holidays.
- Business days: exclude Saturdays and Sundays (and optionally public holidays).
- Leap year adds February 29 — check every year in your date range.
- The [Age Calculator](/calculators/age-calculator) counts total days between any two dates automatically.
Manual counting method
Step 1: Count remaining days in the start month. Step 2: Add full months' days. Step 3: Add days in the final month.
Example: January 15 to April 10. Remaining in January: 31 − 15 = 16 days. February: 28 days (or 29 if leap year). March: 31 days. April 1–10: 10 days. Total: 16 + 28 + 31 + 10 = 85 days.
For multi-year spans, count full years (365 or 366) and add the partial start/end year days.
Calendar days vs. business days
Calendar days include every day — weekends and holidays. "30 calendar days from signing" means exactly 30 days, no exceptions.
Business days (working days) exclude Saturdays and Sundays. A 30-business-day deadline is typically 42 calendar days (6 weeks). Add holidays and it can stretch to 44–45 calendar days.
Legal and financial deadlines almost always specify which type. Read the fine print carefully.
Common use cases
Project management: "The client wants delivery in 90 days." Count 90 calendar days from today to set the deadline.
Pregnancy: due dates are calculated as 280 days (40 weeks) from the first day of the last menstrual period.
Lease agreements: "60-day notice required." Count 60 calendar days backward from move-out to determine the latest notice date.
Visa and travel: many visas count "days in country" within a rolling period (e.g., 90 days within 180 days for Schengen).
Handling leap years
If your date range spans February, check whether the year is a leap year. A leap year occurs when the year is divisible by 4, except centuries not divisible by 400.
If it is a leap year and your range includes February 29, add 1 to your count. If it spans multiple years, check each February.
Example: January 1, 2024 to January 1, 2025. 2024 is a leap year, so the count is 366, not 365.
Try the calculators referenced in this guide
Put the maths into practice — every calculator is free and runs entirely in your browser.
Frequently Asked Questions
Do I count the start date, the end date, or both?
Convention varies. Most "days between" calculations exclude the start date and include the end date. So January 1 to January 3 = 2 days. Our Age Calculator follows this convention.
How do I calculate business days quickly?
Count the weeks and multiply by 5, then add remaining weekdays. For 30 calendar days: 4 weeks (20 business days) + remaining days, minus any weekend days in the remainder.
What is a Julian date?
In astronomy, a Julian date is a continuous count of days since January 1, 4713 BC. In everyday use, "Julian date" sometimes refers to the day of the year (1–365). January 1 = day 1, December 31 = day 365 (or 366).
The Precision Calculator Editorial Team
The editorial team at Get Precision Calculator writes practical, formula-driven guides that explain the maths behind every calculator on this site. All content is reviewed for accuracy before publishing.
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