How do I calculate the hours between two times?

Subtract the start time from the end time. If the end time is earlier than the start time (like an overnight shift), add 24 hours to the end time first so the subtraction works correctly.

How do I convert time to decimal for payroll?

Divide the minutes portion by 60 and add it to the hours. For example, 7 hours 30 minutes becomes 7 + (30 ÷ 60) = 7.5 decimal hours.

How does an overnight shift get calculated correctly?

If the end time (like 6:00 AM) is earlier in the clock than the start time (like 10:00 PM), the calculation adds 24 hours to the end time before subtracting, so the result reflects the true elapsed time rather than a negative number.

How much layover time do I need at the airport?

A common guideline is at least 45-60 minutes for domestic connections and 75-120 minutes for international connections, though larger airports, checked bags, and different terminals or airlines can require more time.

What happens if my time calculation comes out negative?

A negative result usually means the end time is earlier than the start time without accounting for crossing midnight. Most time calculators, including this one, automatically add 24 hours when this happens so the result reflects an overnight span instead of showing a negative number.

How do I subtract a lunch break from work hours?

Calculate the total duration between clock-in and clock-out, then subtract the length of any unpaid break to get net working hours — for example, an 8-hour shift with a 30-minute unpaid lunch results in 7.5 hours of paid time.

What is a comfortable connection time between flights?

For domestic connections, 60-90 minutes is generally comfortable. For international connections, especially ones requiring immigration, customs, or a terminal change, 2-3 hours is a safer buffer.

Time Calculator – Add/Subtract Time, Duration & Layover Checker (Free)

🕐 Time Calculator

Starting Time

Operation

Days / Hours / Minutes

Quick Examples

+8 hr shift from 10 PM +90 min meeting -2 hr from 5 PM

🕐

Enter your times and click Calculate

Your result will appear here.

Calculating…

How It Works

Why Time Math Isn't Regular Subtraction

Time runs in base-60, not base-10, and clocks reset at midnight — that's why a simple subtraction can produce a wrong or negative answer.

Overnight Rule

If End Time < Start Time → add 24 hours to End Time first

This turns an overnight span into an ordinary subtraction that gives the correct positive duration.

Worked Example: 10:00 PM to 6:00 AM Overnight Shift

6:00 AM is earlier than 10:00 PM, so add 24 hours: 6:00 AM becomes 30:00

30:00 − 22:00 = 8 hours

✓ The shift is 8 hours long, not a negative number.

Payroll Reference

Minutes to Decimal Hours Cheat Sheet

Minutes	Decimal Hours
15 min	0.25
30 min	0.50
45 min	0.75
7 hr 30 min	7.50
8 hr 15 min	8.25

Travel Reference

Minimum Connection Times by Airport Type

Connection Type	Minimum	Comfortable
Domestic (same terminal)	30-45 min	60-90 min
Domestic (terminal change)	45-60 min	90 min+
International	75-90 min	2-3 hours
International with re-check-in / customs	2 hours	3+ hours

These are general guidelines, not a guarantee — always check your specific airport's and airline's minimum connection time, especially for large hub airports.

FAQ

Time Calculator — Frequently Asked Questions

Common questions about time math, overnight shifts, and flight connections.