Time Calculator — Add & Subtract Hours, Minutes

Time arithmetic is something we all need but rarely enjoy doing manually. Whether you're scheduling meetings across US time zones, planning cooking times, calculating shift differentials, or figuring out when your flight lands, a time calculator eliminates the mental gymnastics of carrying over minutes and hours. For tracking weekly work hours or daily time card entries, decimal time conversion is especially critical for accurate payroll processing.

How to Add Times

Adding two times (or a time and a duration) follows a simple carry-over process:

1. Add the seconds together. If the result is 60 or more, subtract 60 from the seconds and carry 1 to the minutes.
2. Add the minutes together (plus any carry). If the result is 60 or more, subtract 60 from the minutes and carry 1 to the hours.
3. Add the hours together (plus any carry). If the result is 24 or more, subtract 24 (the time wraps past midnight into the next day).

Example: 10:45:30 PM + 3h 25m 40s

• Seconds: 30 + 40 = 70 → 10 seconds, carry 1
• Minutes: 45 + 25 + 1 = 71 → 11 minutes, carry 1
• Hours: 22 + 3 + 1 = 26 → 26 − 24 = 2:11:10 AM (next day)

If you need to add up multiple time entries for a full workweek, our Hours Calculator handles multi-day spans across date boundaries.

How to Subtract Times

If you're trying to count down the time to an event, you may need to subtract one time from another. You can also use our Days Until Calculator for date-based countdowns. To subtract times, follow these steps:

1. Subtract the seconds. If the result is negative, add 60 to the seconds and borrow 1 from the minutes.
2. Subtract the minutes. If the result is negative, add 60 to the minutes and borrow 1 from the hours.
3. Subtract the hours. If the result is negative, add 24 (the time wraps backward past midnight).

Example: 2:15:00 AM − 4h 30m

• Convert 2:15 AM to 24-hour: 02:15
• Minutes: 15 − 30 = −15 → add 60 = 45 minutes, borrow 1 hour
• Hours: 2 − 1 − 4 = −3 → add 24 = 21:45 = 9:45:00 PM (previous day)

How to Convert a Time to Decimal

Many payroll systems, billing software, and scheduling tools require time in decimal format rather than hours:minutes. Here are the three conversion formulas. In all equations below, H is the number of hours, M is the number of minutes, and S is the number of seconds.

Time to Hours Formula

Use this formula to convert a time to decimal hours — the format most US payroll systems require:

time in hours = H + (M ÷ 60) + (S ÷ 3,600)

Example: 2h 30m 45s → 2 + (30 ÷ 60) + (45 ÷ 3,600) = 2 + 0.5 + 0.0125 = 2.5125 hours

Time to Minutes Formula

Use this formula to convert a time to decimal minutes:

time in minutes = (H × 60) + M + (S ÷ 60)

Example: 2h 30m 45s → (2 × 60) + 30 + (45 ÷ 60) = 120 + 30 + 0.75 = 150.75 minutes

Time to Seconds Formula

Use this formula to convert a time to total seconds:

time in seconds = (H × 3,600) + (M × 60) + S

Example: 2h 30m 45s → (2 × 3,600) + (30 × 60) + 45 = 7,200 + 1,800 + 45 = 9,045 seconds

Decimal Hours to Minutes — Quick Reference Chart

This chart is the quick reference used in US payroll departments to convert clock time to decimal hours. Use it when filling out timesheets or verifying time card calculations.

Tip: 6-minute increments (0.10 hours) are the standard billing unit in the legal profession. Quarter-hour rounding (15 min = 0.25) is the most common US payroll rounding method. Use our Work Hours Calculator to automatically convert your weekly timesheet to decimal format with FLSA overtime.

How to Calculate Time Duration

You can calculate the time duration between two times by following a few steps:

1. Convert both times to 24-hour (military) time. 3:00 PM = 15:00. 8:30 AM = 08:30. Our Military Time Converter handles this instantly.
2. Convert both times to decimal hours. Divide the minutes by 60 to get the decimal portion. 15:00 = 15.0 hours. 08:30 = 8.5 hours.
3. Subtract the start time from the end time. 15.0 − 8.5 = 6.5 hours = 6h 30m

If the end time is before the start time (overnight span), add 24 to the end time first. Example: 10:00 PM to 6:00 AM = (6 + 24) − 22 = 8 hours.

To find the number of days between two dates, use our Date Duration Calculator. For business days only (excluding weekends), use our Business Days Calculator. To find a specific future or past date, try the Date Calculator.

The 7-Minute Rounding Rule for US Payroll

The FLSA (Fair Labor Standards Act) allows employers to round employee clock-in and clock-out times to the nearest increment, as long as the rounding doesn't systematically favor the employer over time. The most widely used method is the 7-minute rule:

• Round to the nearest 15 minutes (quarter hour)
• 1–7 minutes → round down
• 8–14 minutes → round up

Examples:

• Clock in at 8:07 AM → rounds to 8:00 AM
• Clock in at 8:08 AM → rounds to 8:15 AM
• Clock out at 5:22 PM → rounds to 5:15 PM
• Clock out at 5:23 PM → rounds to 5:30 PM

Some employers use 6-minute rounding (tenth of an hour) or exact-minute tracking with digital time clocks. Always verify your company's rounding policy. Use our Time Card Calculator to track your exact clock-in/out times and verify your payroll hours, or the Work Hours Calculator for full weekly timesheet totals with automatic FLSA overtime.

US Time Zones & Daylight Saving Time

Daylight saving time (DST) runs from the second Sunday in March to the first Sunday in November. Arizona (except Navajo Nation) and Hawaii do not observe DST. When scheduling across time zones, remember that the difference between Eastern and Pacific is always 3 hours, regardless of DST. Use our Hours Calculator to compute exact hour differences across multi-day spans, or the Deadline Calculator to find calendar and business-day deadlines from any start date.