Date Calculator - Calculate Days Between Dates

Our free date calculator helps you find the number of days, weeks, months, and years between two dates, add or subtract days from a specific date, and calculate business days excluding weekends and holidays. Perfect for planning events, tracking deadlines, and managing schedules.

What is a Date Calculator?

A date calculator is a versatile tool that performs various date-related calculations:

Calculate duration: Find days, weeks, months, and years between dates
Add days: Find a future date by adding days to a starting date
Subtract days: Find a past date by subtracting days from a starting date
Business days: Calculate working days excluding weekends and holidays
Age calculation: Determine exact age in years, months, and days
Anniversary tracking: Count down to special dates

Add or Subtract Time

Understanding Date Calculations

Days Between Dates

The most common date calculation is finding the difference between two dates:

Example: From January 1, 2026 to December 31, 2026

Days: 364 days
Weeks: 52 weeks
Months: 11 months
Years: 0.997 years

How Date Differences are Calculated

Date calculations account for:

Day count: Total number of days
Leap years: February 29th in leap years
Month lengths: Different number of days per month (28-31)
Time zones: Calculations typically use UTC or local time
Calendar system: Gregorian calendar (standard worldwide)

Common Date Calculation Uses

Planning and Scheduling

Project Management:

Calculate project duration
Track milestone deadlines
Determine completion dates
Schedule task dependencies

Event Planning:

Wedding countdowns
Vacation planning
Conference scheduling
Birthday tracking

Financial Calculations

Loan and Investment:

Calculate loan terms
Track investment periods
Determine interest accrual periods
Plan payment schedules

Business Operations:

Invoice due dates
Contract expiration tracking
Payment terms (Net 30, Net 60)
Fiscal year calculations

Legal and Compliance

Statute of Limitations:

Legal filing deadlines
Contract renewal dates
Compliance reporting periods
Documentation retention periods

Age Verification:

Minimum age requirements
Retirement eligibility
Legal drinking age
School enrollment

Personal Milestones

Age Tracking:

Exact age calculations
Relationship anniversaries
Sobriety milestones
Goal tracking periods

Health and Fitness:

Pregnancy due dates
Medication schedules
Workout program duration
Diet plan tracking

Business Days Calculator

What are Business Days?

Business days (also called working days or weekdays) typically exclude:

Saturdays and Sundays (weekends)
Federal holidays
Company-specific holidays
Observed holidays

Standard business days: Monday through Friday

Common Business Day Uses

Delivery and Shipping:

“Ships in 3-5 business days”
“Delivered within 7 business days”
Return windows (e.g., “30-day return policy”)

Banking and Finance:

Check clearing times
Wire transfer processing
Credit card payment posting
Loan approval timelines

Legal and Contracts:

Response deadlines
Notice periods
Review periods
Appeal windows

US Federal Holidays

Business day calculations typically exclude these 11 federal holidays:

Holiday	Date
New Year’s Day	January 1
Martin Luther King Jr. Day	3rd Monday in January
Presidents’ Day	3rd Monday in February
Memorial Day	Last Monday in May
Juneteenth	June 19
Independence Day	July 4
Labor Day	1st Monday in September
Columbus Day	2nd Monday in October
Veterans Day	November 11
Thanksgiving	4th Thursday in November
Christmas	December 25

Note: When a holiday falls on a weekend, it’s typically observed on the nearest weekday (Friday or Monday).

Calculating Business Days

Example: 10 business days from Monday, January 2, 2026

Counting method:

Week 1: Mon (1), Tue (2), Wed (3), Thu (4), Fri (5)
Weekend: Sat, Sun (not counted)
Week 2: Mon (6), Tue (7), Wed (8), Thu (9), Fri (10)

Result: Friday, January 13, 2026

Leap Years and Date Calculations

What is a Leap Year?

A leap year has 366 days instead of 365, with February having 29 days instead of 28.

Leap Year Rules:

Year divisible by 4 → Leap year
EXCEPT if divisible by 100 → Not a leap year
EXCEPT if divisible by 400 → Leap year

Examples:

2024: Divisible by 4 → Leap year ✓
2000: Divisible by 400 → Leap year ✓
1900: Divisible by 100 but not 400 → Not a leap year ✗
2100: Divisible by 100 but not 400 → Not a leap year ✗

Recent and Upcoming Leap Years

Recent:

2012, 2016, 2020, 2024

Upcoming:

2028, 2032, 2036, 2040

Impact on Date Calculations

Leap years affect calculations spanning February:

Example: January 1 to March 1

Non-leap year (2026): 59 days
Leap year (2024): 60 days

Days in Each Month

Standard (Non-Leap) Year

Month	Days	Abbreviation
January	31	Jan
February	28	Feb
March	31	Mar
April	30	Apr
May	31	May
June	30	Jun
July	31	Jul
August	31	Aug
September	30	Sep
October	31	Oct
November	30	Nov
December	31	Dec

Total: 365 days

Memory Trick: Knuckle Method

Make fists with both hands:

Knuckles: Months with 31 days
Valleys: Months with 30 days (except February)

Left hand: Jan (31), Feb (28/29), Mar (31), Apr (30), May (31), Jun (30), Jul (31) Right hand: Aug (31), Sep (30), Oct (31), Nov (30), Dec (31)

Date Arithmetic Examples

Adding Days to a Date

Example 1: Add 90 days to March 15, 2026

March: 16 days remaining (31 - 15) April: 30 days May: 31 days June: 13 days (16 + 30 + 31 + 13 = 90)

Result: June 13, 2026

Example 2: Add 365 days to February 15, 2024 (leap year)

Result: February 14, 2026 (not February 15 because 2024 has 366 days)

Subtracting Days from a Date

Example 1: Subtract 100 days from May 20, 2026

May: 19 days (20 - 1) April: 30 days March: 31 days February: 20 days (19 + 30 + 31 + 20 = 100)

Result: February 9, 2026

Example 2: Subtract 30 days from January 15, 2026

Result: December 16, 2024 (goes back to previous year)

Calculating Age

Example: Person born on July 15, 1985

As of January 1, 2026:

Years: 39
Months: 5 (July to December = 5 full months)
Days: 17 (from December 15 to January 1)
Total days: 14,414 days

Week Number Calculations

ISO Week Dates

ISO 8601 standard defines week dates:

Week 1: First week with a Thursday in the new year
Weeks start on Monday
Year can have 52 or 53 weeks

Example: 2026 Week Numbers

January 1, 2026 (Wednesday) → Week 1
January 6, 2026 (Monday) → Week 2

Calendar Week vs ISO Week

Calendar week: Sunday to Saturday (US standard) ISO week: Monday to Sunday (International standard)

Differences can cause confusion in international business contexts.

Time Zone Considerations

Date Line and Time Zones

When calculating dates across time zones:

Example:

New York (EST): December 31, 2024, 11:00 PM
Los Angeles (PST): December 31, 2024, 8:00 PM
London (GMT): January 1, 2026, 4:00 AM
Sydney (AEDT): January 1, 2026, 3:00 PM

Impact: Same moment in time, different dates!

UTC (Coordinated Universal Time)

For consistent date calculations:

Use UTC as baseline
Convert local times to UTC
Perform calculation
Convert result back to local time

Historical Calendar Changes

Gregorian Calendar Adoption

The Gregorian calendar (current system) replaced the Julian calendar:

Transition dates varied by country:

Italy, Spain: October 1582 (10 days skipped)
Great Britain, American colonies: September 1752 (11 days skipped)
Russia: February 1918 (13 days skipped)
Greece: March 1924 (13 days skipped)

Impact: Historical date calculations before adoption are complex.

Missing Days in History

When Britain adopted the Gregorian calendar:

September 2, 1752 → September 14, 1752
September 3-13, 1752 never existed in British colonies

Practical Date Calculation Tips

Avoiding Common Mistakes

Exclusive vs Inclusive:
- “From Jan 1 to Jan 10” = 9 or 10 days?
- Clarify if both endpoints count
Month-end issues:
- Adding 1 month to January 31 = February 28/29 (not March 3)
- Be aware of different month lengths
Leap year awareness:
- Check for February 29 in range
- 2000 was a leap year, 1900 was not
Time zone confusion:
- Specify time zone for critical dates
- Use UTC for unambiguous calculations
Business day assumptions:
- Confirm which holidays apply
- Clarify if “business days” or “calendar days”

Quick Mental Calculations

30-day months: April, June, September, November 31-day months: January, March, May, July, August, October, December 28/29-day month: February

Quick age check:

Has birthday passed this year? Age = Current year - Birth year
Birthday not yet passed? Age = Current year - Birth year - 1

Frequently Asked Questions

How many days are there between two dates?

Use a date calculator or manually count, accounting for different month lengths and leap years. Our calculator provides instant results for any date range.

How do I calculate business days?

Count only Monday through Friday, excluding weekends and holidays. For a more accurate calculation, include specific federal or company holidays relevant to your context.

What is the difference between calendar days and business days?

Calendar days include all days (weekends and holidays), while business days typically count only Monday-Friday, excluding holidays. “30 calendar days” = ~30 days. “30 business days” = ~42 calendar days.

How do I add months to a date?

Adding months can be tricky due to varying month lengths. Generally, add the number of months and keep the same day. If the target month has fewer days (e.g., January 31 + 1 month), use the last day of the target month (February 28/29).

Why do some years have 52 weeks and others 53?

A year has 365 days = 52 weeks + 1 day (or 52 weeks + 2 days in leap years). Depending on which day of the week January 1st falls, some years (especially leap years starting on Thursday) have 53 weeks in the ISO week date system.

How accurate are date calculators?

Date calculators are extremely accurate for Gregorian calendar dates (from 1582 onward in most contexts). Historical dates before calendar reforms may require special consideration. Modern date calculators account for leap years automatically.

What’s the maximum date range I can calculate?

Most date calculators can handle dates from 1900 to 2100 or beyond. Practical limitations are minimal for everyday use. Historical dates may require specialized tools.

Do date calculations work across different calendar systems?

This calculator uses the Gregorian calendar, the international standard. Other calendars (Hebrew, Islamic, Chinese) require specialized converters.

Conclusion

Date calculations are essential for planning, scheduling, and tracking time across personal, business, and legal contexts. This free date calculator provides accurate, instant results for days between dates, adding or subtracting days, and calculating business days.

Whether you’re planning a project, tracking an anniversary, calculating legal deadlines, or simply curious about time spans, understanding date arithmetic helps you manage your schedule effectively.

Calculate your dates now and never miss an important deadline or milestone again!

Important Note: This calculator uses the Gregorian calendar and standard calculation methods. For legal, contractual, or official purposes, consult with appropriate professionals to confirm specific date calculations, especially regarding business days and holidays in your jurisdiction. Date calculations involving historical dates before the Gregorian calendar adoption (1582-1924 depending on country) may require specialized tools.