Time Duration Calculator

Calculate the time duration between two times, add or subtract hours, minutes, and seconds. Supports both 12-hour (AM/PM) and 24-hour formats with optional date calculations.

Calculate Time Duration

Quick Answer: Time Duration Calculation

Duration Formula
Duration = End Time - Start Time
Convert to Total Seconds
Seconds = (H x 3600) + (M x 60) + S
12h to 24h (PM)
24h = 12h Time + 12 (except 12 PM)
Common Duration
9 AM to 5 PM = 8 hours
Published By ChallengeAnswer Editorial Team
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Dr. Snezana Lawrence
Dr. Snezana LawrencePhD in Mathematical History
Dr. Snezana Lawrence

Dr. Snezana Lawrence

Mathematical Historian

15+ years experience

PhD from Yale University. Published mathematical historian ensuring precision in all calculations.

Education

PhD in Mathematical History - Yale University

Mathematical HistoryTime CalculationsMathematical Conversions
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Table of Contents

How to Calculate Time Duration

Calculating time duration is essential for tracking work hours, planning schedules, managing projects, and understanding elapsed time between events. Whether you need to calculate payroll hours, meeting lengths, or travel times, understanding time duration calculation is a fundamental skill.

Basic Time Duration Calculation

The simplest way to calculate time duration is to subtract the start time from the end time:

Duration = End Time - Start Time

Example: 5:30 PM - 9:00 AM = 8 hours 30 minutes

Step-by-Step Method

  1. Convert to 24-hour format: 9:00 AM = 09:00, 5:30 PM = 17:30
  2. Subtract hours: 17 - 9 = 8 hours
  3. Subtract minutes: 30 - 0 = 30 minutes
  4. Combine: 8 hours 30 minutes

Handling Borrowing

When end minutes are less than start minutes, borrow from hours:

Example: 3:15 PM - 10:45 AM

15:15 - 10:45
= 14:75 - 10:45 (borrow 1 hour = 60 minutes)
= 4 hours 30 minutes

Calculating Across Midnight

For times that span midnight, add 24 hours to the end time:

Example: 10:00 PM to 6:00 AM

22:00 to 06:00
= (24 + 6) - 22
= 30 - 22
= 8 hours

Pro Tip: For complex calculations involving multiple days, convert everything to total seconds or minutes first, perform the calculation, then convert back to hours, minutes, and seconds.

Understanding Time Formats

Two primary time formats are used worldwide: the 12-hour format (common in the US, Canada, and Australia) and the 24-hour format (used in most other countries and in technical fields).

12-Hour Format (AM/PM)

The 12-hour format divides the day into two 12-hour periods:

  • AM (Ante Meridiem): Midnight (12:00 AM) to 11:59 AM
  • PM (Post Meridiem): Noon (12:00 PM) to 11:59 PM
  • 12:00 AM is midnight (start of day)
  • 12:00 PM is noon (middle of day)

24-Hour Format (Military Time)

The 24-hour format runs continuously from 00:00 to 23:59:

12-Hour24-HourDescription
12:00 AM00:00Midnight
6:00 AM06:00Early Morning
12:00 PM12:00Noon
3:00 PM15:00Afternoon
6:00 PM18:00Evening
11:59 PM23:59Late Night

Conversion Rules

12-Hour to 24-Hour:

  • AM times: Keep the same (except 12 AM = 00:00)
  • PM times: Add 12 (except 12 PM stays 12:00)

24-Hour to 12-Hour:

  • 00:00-11:59: Same time with AM (00:00 = 12:00 AM)
  • 12:00-23:59: Subtract 12 with PM (12:00 stays 12:00 PM)

Practical Applications

Time duration calculations are used in many real-world scenarios. Here are some common applications with examples.

Payroll and Work Hours

Calculating work hours for payroll is one of the most common uses:

Example: Daily Work Hours

  • Clock in: 8:30 AM
  • Lunch break: 12:00 PM - 12:30 PM
  • Clock out: 5:00 PM
Morning: 12:00 PM - 8:30 AM = 3 hours 30 minutesAfternoon: 5:00 PM - 12:30 PM = 4 hours 30 minutesTotal: 3:30 + 4:30 = 8 hours

Project Time Tracking

Track time spent on tasks for project management:

  • Log start and end times for each task
  • Calculate total time per project phase
  • Compare estimated vs. actual time
  • Generate time reports for clients

Travel Planning

Example: Flight Duration

  • Departure: 10:45 AM (New York)
  • Arrival: 2:30 PM (Los Angeles)
  • Note: LA is 3 hours behind NY
Arrival in NY time: 2:30 PM + 3 hours = 5:30 PMFlight duration: 5:30 PM - 10:45 AM = 6 hours 45 minutes

Event Scheduling

Plan events and meetings with precise timing:

  • Calculate meeting durations for calendar blocking
  • Determine break times between sessions
  • Plan travel time between venues
  • Coordinate across time zones

How We Calculate Time Duration

Our calculator uses precise algorithms to calculate time duration accurately, handling all edge cases including midnight crossings, different time formats, and date changes.

Calculation Methodology

1. Time Normalization

All times are first converted to a standard format:

If 12-hour format: Convert to 24-hourCreate timestamp: Date + Hours + Minutes + Seconds

2. Duration Calculation

Calculate the difference in milliseconds:

diffMs = endTimestamp - startTimestamptotalSeconds = diffMs / 1000

3. Unit Conversion

Convert total seconds to days, hours, minutes, seconds:

days = floor(totalSeconds / 86400)hours = floor((totalSeconds % 86400) / 3600)minutes = floor((totalSeconds % 3600) / 60)seconds = totalSeconds % 60

4. Add/Subtract Operations

For adding or subtracting time:

durationMs = (hours * 3600 + minutes * 60 + seconds) * 1000resultTime = baseTimestamp +/- durationMs

Edge Cases Handled

  • Midnight crossing: Automatically detects when end time is before start time
  • Multi-day spans: Accurately calculates durations across multiple days
  • Leap years: Correctly handles February 29th when dates are included
  • Format conversion: Seamlessly converts between 12h and 24h formats

Technical Note: Our calculator uses JavaScript Date objects with millisecond precision. All calculations are performed in the local timezone of your browser.

Frequently Asked Questions

How do I calculate time duration between two times?

To calculate time duration, subtract the start time from the end time. Convert both times to the same format (24-hour is easiest), then subtract hours from hours, minutes from minutes, and seconds from seconds. Borrow from larger units as needed.

What is the difference between 12-hour and 24-hour time format?

12-hour format uses AM/PM to distinguish between morning and afternoon/evening (1:00 AM to 12:59 PM, then 1:00 PM to 12:59 AM). 24-hour format runs from 00:00 to 23:59, where 13:00 equals 1:00 PM, 14:00 equals 2:00 PM, and so on.

How do I convert 12-hour time to 24-hour time?

For AM times: 12:00 AM becomes 00:00, and other AM times stay the same (9:30 AM = 09:30). For PM times: 12:00 PM stays as 12:00, and other PM times add 12 hours (3:45 PM = 15:45).

Can I calculate duration across midnight?

Yes, our calculator handles times that cross midnight. When calculating without dates, if the end time is earlier than the start time, it assumes the end time is on the next day. For precise calculations across multiple days, enable the date option.

How do I add hours and minutes to a time?

To add time, first add the hours to the existing hours, then add minutes to minutes, and seconds to seconds. If minutes exceed 59, carry over to hours. If hours exceed 23, carry over to the next day.

What is the formula to calculate elapsed time?

The formula is: Elapsed Time = End Time - Start Time. Convert both times to total seconds (hours x 3600 + minutes x 60 + seconds), subtract, then convert back to hours:minutes:seconds format.

How many hours are between 9 AM and 5 PM?

There are 8 hours between 9:00 AM and 5:00 PM. In 24-hour format: 17:00 - 09:00 = 8 hours. This is a standard work day duration.

How do I calculate time for payroll purposes?

For payroll, calculate the duration between clock-in and clock-out times, subtract any unpaid breaks. Convert the result to decimal hours for calculations (e.g., 7 hours 30 minutes = 7.5 hours).

What is military time?

Military time is the 24-hour clock format used by armed forces, healthcare, and aviation. It runs from 0000 (midnight) to 2359 (11:59 PM). For example, 0800 is 8:00 AM, 1400 is 2:00 PM, and 2100 is 9:00 PM.

How do I convert minutes to hours and minutes?

Divide the total minutes by 60 to get hours. The remainder is the remaining minutes. For example: 150 minutes / 60 = 2 hours with 30 minutes remaining, so 150 minutes = 2 hours 30 minutes.

Can this calculator handle time zone differences?

This calculator uses local time and does not account for time zone differences. For time zone conversions, first convert both times to the same time zone (like UTC), then calculate the duration.

How accurate is this time duration calculator?

Our calculator is accurate to the second for time duration calculations. It correctly handles day boundaries, leap years when dates are included, and both 12-hour and 24-hour time formats.

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Dr. Snezana Lawrence
Expert Reviewer

Dr. Snezana Lawrence

Mathematical Historian | PhD from Yale

Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.

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