Hours Calculator

Hours calculator at a glance#

How many hours is 9 to 5:30?#

From 9:00 am to 5:30 pm you have 8 hours and 30 minutes, which equals 8.5 hours or 510 minutes. To use the calculator above, input 09:00:00 as the start time and 17:30:00 as the end time.

How do you calculate the hours between two times?#

First, write down both times using the 24-hour clock format. Subtract the start time from the end time, working hour by hour and minute by minute. If the end minutes are less than the start minutes, you’ll need to borrow 1 hour as 60 minutes. The calculator automates this process, displaying the result in hours and minutes, as a clock reading, in decimal hours, and in minutes.

How do you count the hours of an overnight shift?#

To calculate this, add the hours before midnight to the hours after. A shift from 10:00 pm to 6:00 am consists of 2 hours to midnight plus 6 hours after, totaling 8 hours. If the end time is earlier than the start time on the clock, the calculator assumes the shift ends the next day and accounts for time across midnight.

What the hours between two times means#

The hours between two times represent the duration from a start time to an end time on the clock. It's expressed in hours and minutes, such as 8 hours 30 minutes, rather than as a specific time of day.

Most people use the 12-hour clock with am and pm, but it's easier to do arithmetic on the 24-hour clock, where hours range from 00 to 23. Morning times keep their hour unchanged. For afternoon and evening, add 12 to the hour, so 5:30 pm becomes 17:30. Midnight is 00:00 and noon is 12:00. The calculator accepts this 24-hour format as hh:mm:ss (5:30 pm goes in as 17:30:00). You can quickly input these times using the Now, Midnight, and Noon links.

Using 00:00 for midnight avoids common confusion. Since 12 am and 12 pm can be easily mixed up, NIST advises using the 24-hour clock or times such as 11:59 pm and 12:01 am when precision matters.

How to work out the hours by hand#

Consider a shift from 9:00 am to 5:30 pm.

• Convert both times to the 24-hour clock. 9:00 stays 09:00, while 5:30 pm becomes 17:30.
• Subtract the hours: 17 minus 9 gives 8 hours.
• Subtract the minutes: 30 minus 0 gives 30 minutes.

The shift duration is 8 hours and 30 minutes.

If the end minutes are smaller, borrow before subtracting. From 9:45 am to 5:30 pm, since 30 minus 45 isn't possible, write 17:30 as 16 hours and 90 minutes. Then 16 minus 9 gives 7 hours, and 90 minus 45 gives 45 minutes, leading to 7 hours 45 minutes.

To add up the lengths of several shifts, carry every 60 minutes into an hour, as the hours and minutes calculator page shows.

Overnight shifts#

When a shift crosses midnight, the end time is less than the start time on the 24-hour clock, making straightforward subtraction yield a negative. Instead, divide the shift at midnight. From 22:00 to midnight is 2 hours, and from midnight to 06:00 is 6 hours, so the total is 8 hours.

Alternatively, add 24 hours to the end time. 06:00 becomes 30:00, and 30 minus 22 is 8 hours. The calculator follows this logic: if the end time is earlier than the start time, it shifts the end time to the next day before subtracting.

The two times must be within one day of each other. For spans exceeding 24 hours, or for times on different dates, use a calculator that incorporates dates as well as times.

Reading the result#

The calculator presents the time span in four formats. For 9:00 to 17:30, it displays:

• 8 hours 30 minutes, expressed in words.
• 8:30, as a clock reading.
• 8.5 hours, in decimal form.
• 510 minutes, total minutes.

Decimal hours are often used for timesheets and wage calculations since 8.5 can be multiplied by an hourly rate, unlike 8:30. To convert manually, divide the minutes by 60: 30 minutes equals 0.5 hours, 15 minutes is 0.25, and 45 minutes is 0.75. Seconds are also supported. Enter them in the last two digits and they will appear in the result.

Breaks#

The hours calculator computes the entire span between two times. It doesn't deduct breaks automatically, so you need to subtract any unpaid breaks yourself.

Whether a break counts as work time depends on how long it is and whether you are completely relieved from duty.

For a full week's total with a break each day, the work hours calculator includes a start time, an end time, and a break for every day, and its page covers which breaks count as work time.

Where an hours calculator helps#

• Checking a timesheet before submission.
• Determining the length of a shift, class, flight, or meeting from its start and end times.
• Planning sleep: from 11:00 pm to 6:30 am totals 7 hours 30 minutes.
• Billing time to a client in decimal hours.

Hours for common shifts#

These are shift times people often check. The last column takes off a 30-minute unpaid lunch.

Sources#

• NIST, Times of Day FAQs (12 a.m., 12 p.m. and the 24-hour clock)

Frequently asked questions#

How many hours is 8 to 5?#

From 8:00 am to 5:00 pm you have 9 hours. On the 24-hour clock that is 08:00 to 17:00.

How many hours is 10 to 6?#

From 10:00 am to 6:00 pm it's 8 hours. From 10:00 pm to 6:00 am is also 8 hours, counting across midnight.

How many hours is 6 am to 4 pm?#

From 6:00 am to 4:00 pm is 10 hours. On the 24-hour clock that is 06:00 to 16:00.

Is 12 am midnight or noon?#

Typically, 12 am means midnight and 12 pm means noon, but these terms can be mixed up. In the calculator, enter midnight as 00:00:00 and noon as 12:00:00 to remove any uncertainty.

How do I enter pm times?#

Use the 24-hour clock. Add 12 to any hour from 1 pm to 11 pm, making 1:15 pm 13:15:00 and 5:30 pm 17:30:00. Times from 1:00 am to 11:59 am remain unchanged, and 12:30 am is 00:30:00.

Does the hours calculator subtract my lunch break?#

No. It calculates the entire time between the two times. You need to manually subtract any unpaid breaks or use the work hours calculator, which includes a break field for each day.

Can I calculate more than 24 hours?#

Not with just two clock times, as they can only be within one day of each other. For longer spans, enter the start and end dates along with the times in a time duration calculator.