Hours Calculator

What Is an Hours Calculator?

An hours calculator finds the number of hours and minutes between two points in time. It eliminates the manual arithmetic involved in time subtraction - a process that trips up many people because time uses base-60 (not base-10) math, and because AM/PM conventions add another layer of potential error.

This page provides two hours calculators:

• Hours Between Two Times: Enter a start time and end time (in 12-hour AM/PM format) to find the elapsed hours and minutes. If the end time is earlier than the start time on the clock, the calculator automatically assumes the end time is on the following day - handling overnight shifts without any special input.
• Hours Between Two Dates: Enter a full start date and time and end date and time to calculate the exact number of hours between them - spanning any number of days, weeks, or months.

Both calculators display the result in multiple formats: hours and minutes (e.g., 8 hours 45 minutes), decimal hours (e.g., 8.75 hours), total minutes, and total seconds - making it easy to use the result directly in payroll, billing, or scheduling systems.

How to Calculate Hours Between Two Times Manually

Understanding the manual method helps you catch errors and understand what the calculator is doing:

1. Convert both times to 24-hour format. AM hours stay the same (except 12 AM → 0). PM hours: add 12 (except 12 PM stays 12). Example: 9:15 AM → 9:15; 5:45 PM → 17:45.
2. Subtract start from end. 17:45 − 9:15: first the minutes (45 − 15 = 30), then the hours (17 − 9 = 8). Result: 8 hours 30 minutes.
3. Handle minute borrowing if needed. If the end minutes are smaller than the start minutes, borrow 1 hour (60 minutes) from the hours column. Example: 5:10 PM − 9:40 AM → 17:10 − 9:40: minutes: 10 − 40 requires borrowing → (60 + 10) − 40 = 30 minutes; hours: (17 − 1) − 9 = 7 hours. Result: 7 hours 30 minutes.
4. Handle overnight spans. If the end time is earlier than the start time (e.g., 10:00 PM to 6:00 AM), add 24 hours to the end time before subtracting: 6:00 AM = 6:00 → 6 + 24 = 30:00; 30:00 − 22:00 = 8 hours.

Decimal Hours vs. Hours and Minutes

Time can be expressed in two common formats, and knowing how to convert between them is essential for payroll, billing, and scheduling:

• Hours and minutes (HH:MM): The natural human format. 8 hours 45 minutes, 7 hours 30 minutes.
• Decimal hours: Used in payroll systems, billing software, and spreadsheets. 8.75 hours, 7.5 hours.

To convert HH:MM to decimal hours: divide the minutes by 60 and add to the hours.

HH:MM	Decimal Hours	Calculation
1:00	1.000	1 + 0/60
1:15	1.250	1 + 15/60
1:30	1.500	1 + 30/60
1:45	1.750	1 + 45/60
7:20	7.333	7 + 20/60
8:45	8.750	8 + 45/60
10:06	10.100	10 + 6/60

To convert decimal hours back to HH:MM: take the whole number as hours, multiply the decimal part by 60 to get minutes. Example: 8.75 hours → 8 hours and (0.75 × 60) = 45 minutes → 8:45.

Tracking Work Hours and Time Sheets

Hours calculators are most commonly used for time sheet tracking - recording start and end times for each shift and totaling hours worked for payroll. Accurate time tracking matters because:

• Payroll is calculated on hours worked, often in decimal form (40.25 hours × $18.50/hr)
• Overtime eligibility is determined by whether weekly hours exceed a threshold (40 hours under US federal law)
• Project billing often requires logging hours worked per client or task
• Compliance with labor laws requires documentation of hours in certain industries

Calculating Total Weekly Hours: Example Time Sheet

An employee works the following schedule in a week:

Day	Start	End	Break	Hours Worked
Monday	8:00 AM	5:00 PM	1 hr	8:00
Tuesday	8:30 AM	6:00 PM	30 min	9:00
Wednesday	9:00 AM	5:30 PM	1 hr	7:30
Thursday	8:00 AM	6:30 PM	1 hr	9:30
Friday	8:00 AM	4:00 PM	30 min	7:30
Total				41:30 = 41.5 hrs

This employee worked 41.5 hours - 1.5 hours of overtime. At a regular rate of $20/hr, with overtime at 1.5× ($30/hr): (40 × $20) + (1.5 × $30) = $800 + $45 = $845 gross pay.

Break and Lunch Deductions

Most employers deduct unpaid meal breaks from the total hours worked. How breaks are handled varies:

• Unpaid meal breaks: Typically 30–60 minutes, not counted as work time. An employee clocked 9:00 AM–5:00 PM with a 30-minute unpaid lunch worked 7.5 hours, not 8.
• Paid rest breaks: Short breaks of 5–20 minutes are generally considered compensable work time under US federal law and must be included in total hours worked.
• Auto-deduct policies: Some employers automatically deduct a set break period (e.g., 30 minutes) from every shift over a certain length, regardless of whether the employee actually took a break. This can cause disputes if breaks were missed.

To calculate net hours after a break deduction: subtract the break duration from the gross shift duration. For a 8:00 AM–5:00 PM shift with a 45-minute unpaid lunch: gross = 9:00, net = 9:00 − 0:45 = 8 hours 15 minutes = 8.25 hours.

Overtime Rules and Hours Thresholds

In the United States, the Fair Labor Standards Act (FLSA) requires that non-exempt employees be paid at least 1.5 times their regular rate for any hours worked over 40 in a workweek. Key points:

• The 40-hour threshold is weekly, not daily. Working 10 hours on Monday does not trigger overtime by itself - only when cumulative weekly hours exceed 40.
• Some states have daily overtime rules. California, for example, requires overtime for any hours worked beyond 8 in a single day, and double time for more than 12 hours in a day.
• Exempt employees (those meeting the FLSA's salary and duties tests, generally earning at least $684/week) are not entitled to overtime pay regardless of hours worked.
• Double time may apply for work on holidays or for very long shifts in some states and under certain union contracts.

Hours Worked (weekly)	Pay Rate (US federal)
0–40 hours	Regular rate (1×)
41+ hours	Overtime rate (1.5×)
CA: 0–8 hrs/day	Regular rate (1×)
CA: 8–12 hrs/day	Overtime rate (1.5×)
CA: 12+ hrs/day	Double time (2×)

Night Shifts and Overnight Hours

Overnight shifts - where the end time is on the next calendar day - require special handling. The "Hours Between Two Times" calculator automatically detects when the end time is earlier than the start time and adds 24 hours, correctly computing the span. For example:

• Start: 10:00 PM, End: 6:00 AM → Calculator adds 24 to end: 6:00 AM is treated as 30:00, giving 30:00 − 22:00 = 8 hours.
• Start: 11:30 PM, End: 7:15 AM → 31:15 − 23:30 = 7 hours 45 minutes.

For multi-day spans, use the "Hours Between Two Dates" calculator, which accepts full date inputs and computes the exact difference in hours regardless of how many days, weeks, or months separate the two timestamps.

The 12-Hour Clock (AM/PM)

A 12-hour clock uses the numbers 1–12 to represent the hours of the day. Each full day is divided into two cycles: AM and PM. AM stands for ante meridiem, a Latin phrase meaning "before midday," while PM stands for post meridiem, meaning "after midday." Each cycle runs for 12 hours, making a total of 24 hours in a day.

By convention, 12 AM denotes midnight (the start of a new calendar day), while 12 PM denotes noon. This can cause confusion - a meeting scheduled for "12 PM" is at noon, while "12 AM" is midnight. The transition from AM to PM occurs at noon, and from PM to AM occurs at midnight.

The 12-hour clock is the most widely used format in the United States, Canada, Australia, and several other countries. Times are typically written with a colon between hours and minutes (e.g., 3:45 PM).

The 24-Hour Clock (Military Time)

A 24-hour clock uses the numbers 0–23, where 00:00 indicates midnight, 12:00 indicates noon, and 23:59 is one minute before the next midnight. Unlike the 12-hour clock, it does not repeat numbers within a day, eliminating the need for AM and PM designations entirely.

This format is an international standard (ISO 8601) and the default in most countries outside of North America. It is the standard in scientific, military, aviation, medical, and computing contexts. Converting between the two systems:

12-Hour	24-Hour	12-Hour	24-Hour
12:00 AM (midnight)	00:00	12:00 PM (noon)	12:00
1:00 AM	01:00	1:00 PM	13:00
6:00 AM	06:00	6:00 PM	18:00
9:30 AM	09:30	9:30 PM	21:30
11:59 AM	11:59	11:59 PM	23:59

Rule: For AM, the hour is the same (except 12 AM → 00). For PM, add 12 to the hour (except 12 PM → 12).

Hours in Different Time Periods

Time Period	Hours	Notes
1 hour	1	60 minutes = 3,600 seconds
1 day	24	1,440 minutes = 86,400 seconds
1 week	168	7 days × 24 hours
1 month (avg.)	730.5	Range: 672 (Feb) to 744 (31-day month)
1 year (common)	8,760	365 days × 24 hours
1 year (leap)	8,784	366 days × 24 hours
1 decade	~87,660	Avg. across 10-year span
1 century	~876,600	Avg. across 100-year span
Standard work year	2,080	40 hrs/wk × 52 weeks
Standard work month	~173.3	2,080 ÷ 12

Hours in Professional and Industry Contexts

Different fields have specific conventions for how hours are tracked and reported:

• Healthcare: Hospital shifts are typically 8 or 12 hours. The 12-hour shift structure (3 shifts per week) has become dominant in nursing. Resident physicians may work up to 80 hours per week under ACGME (Accreditation Council for Graduate Medical Education) duty hour restrictions.
• Aviation: Pilot duty time is strictly regulated. Under FAA rules, airline pilots are generally limited to 8 flight hours in a 24-hour period, 9 hours for certain short-haul operations, and a maximum of 100 flight hours in any 672 consecutive hours (28 days).
• Legal billing: Attorneys typically bill in tenths of an hour (6-minute increments). A 25-minute phone call is billed as 0.4 hours (rounded up to the nearest tenth). This makes decimal hours essential for legal time tracking.
• Construction: Job sites typically run 10-hour days, 4 days per week (the "4-10" schedule), keeping workers at 40 hours per week while providing a three-day weekend. Any work beyond 40 hours triggers overtime pay requirements.
• Education: A "credit hour" in higher education is defined as one hour of classroom instruction per week for 15 weeks per semester. A full-time student taking 15 credit hours spends approximately 15 hours per week in class (plus an expected 30 hours of independent study).

Frequently Asked Questions