Time Calculator

Add & subtract time — find duration between dates — convert formats — calculate work hours and pay.

Starting time

Hours

Minutes

Seconds

Operation

Amount to add / subtract

Hours

Minutes

Seconds

Result wrapping

From date & time

To date & time

Mode

Time to convert

Hours

Minutes

Seconds

Time format

Clock in

Clock out

Clock in (24-hr)

Clock out (24-hr)

Break time (minutes)

Hourly rate (optional)

Overnight shift?

How Time Math Works

Time arithmetic is base-60 for minutes and seconds (values 0–59) and base-24 or base-12 for hours. Adding 50 minutes to 9:20 produces 10:10, not 9:70 — the carry rules are the same as regular addition but with different base boundaries. The most reliable approach converts everything to total seconds, performs the math, then converts back.

Decimal Hours — the Payroll Standard

Decimal hours express any time as a fraction of one hour. Divide minutes by 60: 30 min = 0.50, 45 min = 0.75, 15 min = 0.25. At $20/hr, 8.75 decimal hours pays exactly $175 — far simpler than calculating hours and minutes separately.

Minutes	Decimal	Minutes	Decimal
15 min	0.2500	40 min	0.6667
20 min	0.3333	45 min	0.7500
30 min	0.5000	50 min	0.8333

24-Hour vs 12-Hour Format

The 24-hour (military) clock runs from 00:00 to 23:59 with no AM/PM. To convert 24-hr to 12-hr: subtract 12 from any hour over 12, or use 12 for noon and 12 AM for midnight. Hours 1–11 stay the same (AM); 13–23 become 1–11 PM.

24-hour	12-hour	24-hour	12-hour
00:00	12:00 AM	13:00	1:00 PM
09:00	9:00 AM	17:30	5:30 PM
12:00	12:00 PM	23:59	11:59 PM

Frequently Asked Questions

How do I add hours and minutes together?

Use Add & Subtract mode. Enter your starting time in HH:MM:SS, select “Add time,” enter the duration to add, and click Calculate. Carries are handled automatically.

How do I calculate work hours across midnight?

Use Work Hours mode and toggle “Crosses midnight.” Enter clock-in (e.g. 10:00 PM) and clock-out (e.g. 6:30 AM). The overnight flag adds 24 hours to the clock-out before computing the gap.

What is 8 hours 45 minutes as a decimal?

8.75 decimal hours. Formula: 45 ÷ 60 = 0.75, so 8 + 0.75 = 8.75. Use Convert & Decimal mode with “Time → Decimal” to verify instantly.

How do I convert 14:30 to 12-hour format?

Use Convert & Decimal → All Formats. Enter 14 hours, 30 minutes, 0 seconds. The result instantly shows 2:30:00 PM alongside every other format.