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Time Duration Calculator

Calculate the exact duration between two dates and times. Get results in years, months, weeks, days, hours, minutes, and seconds. Free online time calculator.

Last revised 2 September 2026

By Team GlobalCalqulate · About our editorial standards

Start Date & Time

Start Date

Select the starting date.

Start Time

Select the starting time (optional, requires 'Include Time' to be enabled).

End Date & Time

End Date

Select the ending date.

End Time

Select the ending time (optional).

Duration

0 years, 11 months, 30 days

364 days

Methodology

Formula:: Duration
Content last updated:: September 2026
Scheduled re-verification:: September 2027

Calculation type: Exact calculation.

Formula & methodology

Formula used

Duration

duration = end date-time − start date-time

The elapsed time between two moments, computed in milliseconds and then broken into units.

Unit breakdown

days = ms ÷ 86,400,000;  hours = ms ÷ 3,600,000;  minutes = ms ÷ 60,000

Each unit is a conversion of the same underlying millisecond difference.

Variable definitions

Symbol	Meaning	Unit
start	Start date and time. the beginning of the interval	date-time
end	End date and time. the end of the interval	date-time

Step-by-step calculation

1. Enter the start and end
The end must be after the start.
2. Include times for a precise duration
Without times both ends are treated as midnight.

Limitations

Both moments are treated as being in the same time zone. An interval spanning zones needs the times converted first.
Daylight-saving changes can make the wall-clock difference and the true elapsed time differ by an hour.
Leap seconds are not modelled.

This page is educational. It applies the formula described above to the figures you enter and shows the arithmetic behind the result. The output is only as good as the inputs and the assumptions listed here, and it is general information rather than advice about your particular situation.

Help & FAQs

Frequently Asked Questions

Clear answers to common questions to help you use this calculator confidently.

How do I calculate the time between two dates?

Tap to view the answer

Enter the start and end dates (with optional times) into the calculator. It will automatically compute the duration in years, months, weeks, days, hours, minutes, and seconds.

Does this calculator account for leap years?

Tap to view the answer

Yes. The calculator automatically accounts for leap years, varying month lengths, and daylight saving time differences for accurate duration calculations.

Can I include time in the calculation?

Tap to view the answer

Yes. Toggle 'Include Time in Calculation' and enter start and end times. This provides precision down to seconds, which is useful for exact interval measurements.

What's the difference between total months and 'years, months, days'?

Tap to view the answer

Total months is the entire duration expressed in months (e.g., 18 months). 'Years, Months & Days' breaks it down into a human-readable format (e.g., 1 year, 6 months, 0 days).

How accurate is the time duration calculation?

Tap to view the answer

Duration calculations are accurate to the second when time is included. Month and year approximations use standard astronomical values (30.44 days/month, 365.25 days/year) for consistency.

Need more help? Contact support or email globalcalqulate@gmail.com

We typically reply within 24–48 hours.

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How to Use This Calculator

Enter Start Date & Time

Choose the beginning date and optional start time.

Enter End Date & Time

Choose the ending date and optional end time.

Toggle Time Inclusion

Enable time inclusion for precise hour/minute/second calculations.

View Duration Results

See the duration in multiple units: years, months, weeks, days, hours, minutes, seconds.

Understanding Your Results

Years, Months & Days
The duration broken down into full years, remaining months, and remaining days for a human-readable format.
Total Days
The complete duration expressed in days, calculated by converting all larger units into days.
Total Hours / Minutes / Seconds
When time is included, the total duration is also shown in hours, minutes, and seconds for precise intervals.

Key Tips

✓
Include time for precise calculations down to the second.
✓
The calculator handles leap years and month length variations automatically.
✓
Use total days for contract or billing period calculations.
✓
Years, Months & Days format is ideal for age calculations.
✓
The calculator supports dates from 1900 to 2100.

Understanding Time Duration Calculations

What is Time Duration?

Time duration is the measurement of elapsed time between two points. It can be expressed in various units including years, months, weeks, days, hours, minutes, and seconds depending on the precision needed.

How Duration is Calculated

The calculator first determines the total number of seconds between the two dates/times. It then converts this into larger units: seconds → minutes → hours → days → weeks → months → years. Leap years and varying month lengths are accounted for automatically.

Precision and Rounding

Duration calculations use exact arithmetic where possible. Months are approximated at 30.44 days, years at 365.25 days to account for leap years. For precise legal or financial durations, use total days or hours.

Common Use Cases

Time duration calculations are used for age calculation, project timelines, contract durations, billing periods, countdowns to events, employment tenure, and academic course durations.

Formula & methodology

Formula used

Duration

duration = end date-time − start date-time

The elapsed time between two moments, computed in milliseconds and then broken into units.

Unit breakdown

days = ms ÷ 86,400,000;  hours = ms ÷ 3,600,000;  minutes = ms ÷ 60,000

Each unit is a conversion of the same underlying millisecond difference.

Variable definitions

Symbol	Meaning	Unit
start	Start date and time. the beginning of the interval	date-time
end	End date and time. the end of the interval	date-time

Step-by-step calculation

1. Enter the start and end
The end must be after the start.
2. Include times for a precise duration
Without times both ends are treated as midnight.

Limitations

Both moments are treated as being in the same time zone. An interval spanning zones needs the times converted first.
Daylight-saving changes can make the wall-clock difference and the true elapsed time differ by an hour.
Leap seconds are not modelled.

Calculator inputs

Start Date & Time

End Date & Time

Your results

Methodology

Formula & methodology

Formula used

Duration

Unit breakdown

Variable definitions

Step-by-step calculation

Limitations

How do I calculate the time between two dates?

Does this calculator account for leap years?

Can I include time in the calculation?

What's the difference between total months and 'years, months, days'?

How accurate is the time duration calculation?

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Calculator inputs

Start Date & Time

End Date & Time

Your results

Methodology

How to Use This Calculator

Example: Duration from Jan 1 to Dec 31, 2025 (9 AM to 5 PM)

Understanding Your Results

Key Tips

Understanding Time Duration Calculations

What is Time Duration?

How Duration is Calculated

Precision and Rounding

Common Use Cases

Formula & methodology

Formula used

Duration

Unit breakdown

Variable definitions

Step-by-step calculation

Limitations

How to Use This Calculator

Example: Duration from Jan 1 to Dec 31, 2025 (9 AM to 5 PM)

Understanding Your Results

Key Tips

Understanding Time Duration Calculations

What is Time Duration?

How Duration is Calculated

Precision and Rounding

Common Use Cases