Please enter a valid start date.
The earlier or first date
Please enter a valid end date.
The later or second date
Total Calendar Days
—
—
Was this calculator helpful?
Was this calculator helpful?
Sources & Methodology
Day-count calculations use the proleptic Gregorian calendar as defined by ISO 8601 and verified against NIST civil time standards. Business day counts follow the Monday–Friday convention per U.S. Department of Labor guidelines.
NIST — Civil Time & Gregorian Calendar
National Institute of Standards and Technology reference for the Gregorian calendar rules including leap year determination used in all date arithmetic on this page.
ISO 8601 — Date and Time Standard
International standard for representing dates and calculating date intervals, used to define the start-inclusive, end-exclusive day counting convention applied here.
U.S. Dept. of Labor — FLSA Workweek Definition
Reference for the Monday–Friday business day definition and workweek structure used in the business days calculation.
Methodology: Both dates are parsed to UTC midnight to eliminate daylight-saving-time offsets. Total days = (End − Start) ÷ 86,400,000 ms, floored to an integer. Weeks = floor(days ÷ 7). Calendar months = calendar month boundary count between dates. Business days: iterate each day in range; count days where day-of-week is Monday (1) through Friday (5). Weekend days = total days − business days. Leap years handled automatically by the JavaScript Date object using the proleptic Gregorian calendar.
⏱ Last reviewed: April 2026
How to Count Days Between Two Dates
Counting the days between two dates is one of the most common everyday calculations — for deadlines, rental periods, legal timeframes, project milestones, and event countdowns. While simple in concept, it requires care around month-length variations, leap years, and whether the start and end dates themselves are included in the count.
The Day-Count Formula
Total Days = (End Date − Start Date) in milliseconds ÷ 86,400,000
Weeks = floor(Total Days ÷ 7) | Remaining Days = Total Days mod 7
Business Days = count of Mon–Fri days in the range
Example: January 1 to March 31 (non-leap year)
January: 31 days, February: 28 days, March: 30 days (up to Mar 30)
Total = 89 days | 12 weeks 5 days | ~64 business days
January: 31 days, February: 28 days, March: 30 days (up to Mar 30)
Total = 89 days | 12 weeks 5 days | ~64 business days
Days in Each Month — Reference
| Month | Days (normal) | Days (leap year) | Cumulative Day of Year |
|---|---|---|---|
| January | 31 | 31 | 1–31 |
| February | 28 | 29 | 32–59 (60) |
| March | 31 | 31 | 60–90 (91) |
| April | 30 | 30 | 91–120 (121) |
| May | 31 | 31 | 121–151 |
| June | 30 | 30 | 152–181 |
| July | 31 | 31 | 182–212 |
| August | 31 | 31 | 213–243 |
| September | 30 | 30 | 244–273 |
| October | 31 | 31 | 274–304 |
| November | 30 | 30 | 305–334 |
| December | 31 | 31 | 335–365 (366) |
Calendar Days vs Business Days
Calendar days count every day including Saturdays, Sundays, and public holidays. Business days (also called working days or weekdays) count only Monday through Friday. A 14-calendar-day period starting on a Monday contains exactly 10 business days — two complete workweeks. Business days are used in legal notices, shipping estimates, contract timelines, and financial settlement periods. This calculator shows both counts simultaneously.
When to Count Inclusively vs Exclusively
There are two conventions for counting days between dates. The exclusive-end method (the default here) counts January 1 to January 5 as 4 days — the number of complete days that pass. The inclusive method counts both the start and end date, giving 5 days. Which to use depends on context:
- Exclusive-end: Age calculations, project durations, shipping transit time
- Inclusive: Hotel stays (check-in day + check-out day both counted), legal deadlines where "within 30 days" includes both day 1 and day 30, event duration ("a 3-day festival" running Friday, Saturday, Sunday)
Common Day-Count Reference Points
| Period | Calendar Days | Business Days (approx) |
|---|---|---|
| 1 week | 7 | 5 |
| 2 weeks | 14 | 10 |
| 1 month (avg) | 30–31 | ~21–23 |
| 1 quarter (3 months) | 90–92 | ~65 |
| 6 months | 181–184 | ~130 |
| 1 year (non-leap) | 365 | ~261 |
| 1 year (leap) | 366 | ~262 |
💡 Excel Tip: To count days between two dates in Excel, simply subtract one date cell from another: =B1-A1. Format the result as a number (not a date). For business days use =NETWORKDAYS(A1,B1)-1 (the -1 excludes the start date). For total days including both start and end: =B1-A1+1.
Frequently Asked Questions
Convert both dates to a common numeric form (milliseconds since a fixed point), subtract the earlier from the later, then divide by 86,400,000 (ms per day) and floor the result. This gives calendar days from start to end, not counting the start day itself. For example, January 1 to January 8 = 7 days (one week). The calculator does this instantly for any date pair.
January: 31, February: 28 (29 in leap years), March: 31, April: 30, May: 31, June: 30, July: 31, August: 31, September: 30, October: 31, November: 30, December: 31. Memory trick: make a fist — knuckles are 31-day months (Jan, Mar, May, Jul, Aug, Oct, Dec), valleys between knuckles are shorter months. February is always the shortest.
Count only Monday through Friday within the date range. For complete weeks, each contributes 5 business days. For partial weeks, count Mon–Fri days individually. A simple approximation: Business Days ≈ (Total Days × 5) ÷ 7. For exact counts (required for legal or financial use), this calculator iterates every day in the range and counts weekdays precisely.
Use the quick preset buttons above to set today as start, then enter your target date as the end. The calculator shows the exact number of days remaining. For a manual estimate: days left in this month + days in each complete month between + day number in the target month. The calculator gives the precise answer instantly.
By default this calculator uses the exclusive-end convention: the start date is counted, the end date is not. So January 1 to January 5 = 4 days. Some contexts use inclusive counting (both start and end counted), giving 5 days. Hotel stays, legal deadlines, and event durations often use inclusive counting. The inclusive count is simply the calendar day result plus one.
If the range includes February 29 (a leap day), the total is one day higher than a non-leap equivalent. Leap years occur every 4 years (2024, 2028, 2032...) except century years not divisible by 400. So 2000 was a leap year, but 1900 and 2100 are not. This calculator handles all leap year rules automatically using the built-in date engine.
A standard year has 365 days. A leap year has 366 days. The average Gregorian calendar year is 365.2425 days. For multi-year spans, always calculate using actual dates rather than multiplying by 365, because the number of leap years in your range affects the exact total. A 4-year span from Jan 1, 2021 to Jan 1, 2025 = 1,461 days (one leap year: 2024).
Calendar days include every day — Monday through Sunday, weekdays and weekends, holidays and non-holidays. Business days count only Monday through Friday (weekdays), excluding weekends. They may also exclude public holidays, though this calculator does not subtract holidays since these vary by country and region. A 30-calendar-day month contains roughly 21–22 business days.
Simplest method: =B1-A1 (where A1 is start date, B1 is end date) — format result as a number. For business days: =NETWORKDAYS(A1,B1)-1 (excludes the start day). For inclusive count: =B1-A1+1. For years-months-days breakdown: use =DATEDIF(A1,B1,"Y") for years, =DATEDIF(A1,B1,"YM") for remaining months, =DATEDIF(A1,B1,"MD") for remaining days.
Use the quick preset button above or enter today as start and December 25 as end. As reference points: from January 1, there are 358 days to Christmas (359 in a leap year). From July 4 (US Independence Day) there are roughly 174 days. From Halloween (October 31) there are exactly 55 days to Christmas.
Enter today as the start date and January 1 of the next year as the end. The exact count depends on the current date. As reference points: from December 1 there are 30 days to Jan 1. From October 1 there are 91 days. From July 1 there are 183 days (184 in a leap year). Use the Year to Date preset and swap the dates to count days remaining in the year.
Related Calculators
Popular Calculators
Dog Years Calculator
Everyday Life
Hours From Calculator
Everyday Life
Military Time Converter
Everyday Life
Speed Distance Time Calculator
Everyday Life
Stripe Fee Calculator
Finance
Pain & Suffering Calculator
Legal
TDEE Calculator
Health
Roofing Calculator
Construction
GPA Calculator
Education
Mortgage Refinance Calculator
Finance
CPM Calculator
Marketing
Markup Calculator
Finance