To add hours and minutes: sum the minutes separately, convert every 60 minutes to 1 hour, then add the resulting hours. 3:45 + 2:30 = 5h 75min = 6 hours 15 minutes. To convert decimal hours: the whole number is hours; multiply the decimal by 60 for minutes. 7.75 hours = 7 hours 45 minutes. Time uses base-60, not base-10 — you cannot simply add 3.45 + 2.30 in decimal.
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What Is an Hours Calculator?
An hours calculator adds, subtracts, and totals time entries expressed in hours and minutes, and converts between hours:minutes format and decimal hours. It is used for payroll timesheets, project time tracking, billing, and any situation where you need to sum multiple time durations accurately.
The challenge with time math is that it uses base-60 arithmetic, not base-10. When you add 8 hours 45 minutes and 6 hours 50 minutes, you cannot treat them as decimal numbers (8.45 + 6.50 = 14.95 is wrong). The correct process: add minutes separately (45 + 50 = 95 minutes), convert the overflow (95 min = 1h 35min), then add the hours (8 + 6 + 1 = 15 hours 35 minutes).
Payroll and billing systems typically require decimal hours rather than hours:minutes. Converting is simple: Decimal = Hours + (Minutes ÷ 60). So 7 hours 45 minutes = 7 + (45 ÷ 60) = 7.75 hours. The reverse: take the decimal part and multiply by 60 to get minutes.
The calculator also handles clock-in/clock-out calculations, automatically subtracting break time and totaling hours across multiple days — the most common use case for weekly timesheets. It then multiplies total hours by an hourly rate to compute gross pay, including overtime at 1.5× for hours beyond 40.
Adding Hours and Minutes
Method 1: Add hours and minutes separately
8 h 45 min
+ 6 h 50 min
-----------
14 h 95 min = 14 h + 1 h 35 min = 15 h 35 min
Method 2: Convert everything to minutes first 8h 45m = 525 min 6h 50m = 410 min Total: 935 min = 935/60 = 15h 35min
Timesheet calculation example:
| Day | Clock In | Clock Out | Lunch | Hours Worked | |-----|---------|---------|-------|-------------| | Mon | 8:00 AM | 5:30 PM | 30 min | 9:00 | | Tue | 8:15 AM | 5:00 PM | 45 min | 8:00 | | Wed | 7:45 AM | 6:00 PM | 30 min | 9:45 | | Thu | 8:30 AM | 5:30 PM | 60 min | 8:00 | | Fri | 8:00 AM | 4:30 PM | 30 min | 8:00 | | Total | | | | 42:45 |
42 hours 45 minutes = 42.75 hours for payroll purposes.
Decimal Hours vs. Hours:Minutes
Payroll, billing, and project management systems often use decimal hours (3.5 hours) instead of hours:minutes (3:30). Conversion:
Hours:Minutes → Decimal: Decimal = Hours + (Minutes / 60)
Decimal → Hours:Minutes: Minutes = Decimal fractional part × 60
Quick reference:
| Hours:Min | Decimal | Hours:Min | Decimal | |---------|---------|---------|---------| | 0:15 | 0.25 | 4:00 | 4.00 | | 0:30 | 0.50 | 4:30 | 4.50 | | 0:45 | 0.75 | 5:00 | 5.00 | | 1:00 | 1.00 | 7:30 | 7.50 | | 1:30 | 1.50 | 7:45 | 7.75 | | 2:00 | 2.00 | 8:00 | 8.00 |
Calculating Pay from Hours
Regular pay = Hours worked × Hourly rate
Overtime = Max(0, Hours − 40) × Hourly rate × 1.5
Total pay = Regular hours pay + Overtime pay
For 42.75 hours at $20/hour:
- Regular: 40 hours × $20 = $800
- Overtime: 2.75 hours × $30 = $82.50
- Total: $882.50
Frequently Asked Questions
Why can't I just add 3:45 + 2:30 = 6:15 in Excel? Spreadsheet programs store time as a fraction of 24 hours — 1 hour = 1/24 = 0.04167. When you add time cells, you're adding these fractions, which works correctly for times within a day. For elapsed hours totaling over 24, format the result cell as [h]:mm (with brackets around h) to show total hours rather than wrapping around midnight. Otherwise 25 hours would display as 1:00 (1 AM the next day).
How do I calculate hours worked from clock-in/clock-out times? Clock-out − Clock-in = total duration. Subtract any unpaid break time. For example: Clock in 8:00 AM, Clock out 5:30 PM = 9.5 hours total. Minus 30-minute lunch = 9.0 hours worked = 9:00. Be consistent about whether break time is paid or unpaid — the FLSA requires tracking compensable time but does not dictate how breaks are recorded.
How many hours is a part-time job vs. full-time? Under the Affordable Care Act, full-time employment is defined as 30+ hours per week for benefits eligibility purposes. For traditional purposes, full-time is typically 35–40 hours/week. Part-time is anything under full-time, commonly 15–30 hours/week. Overtime pay under the FLSA kicks in at 40+ hours/week (not 35+) for non-exempt employees.
How do I convert between time zones for scheduling? Time zone conversion is not just addition/subtraction — it also involves Daylight Saving Time (DST) transitions. For example, New York is UTC−5 (EST) in winter and UTC−4 (EDT) in summer. London is UTC+0 (GMT) in winter and UTC+1 (BST) in summer. The offset between them changes at DST transitions. For reliable conversion, use a time zone converter tool that accounts for DST.
How many hours are in a year? 365 days × 24 hours = 8,760 hours/year. In a leap year: 366 × 24 = 8,784 hours. A standard work year (40 hours/week × 52 weeks) = 2,080 hours. Accounting for 10 paid holidays: 2,080 − (10 × 8) = 2,000 billable hours. This is why consultants often quote rates with "up to 2,000 billable hours/year" as the practical maximum.
Related Free Tools on RoughTools
- Time Zone Converter — convert times between time zones
- Paycheck Calculator — calculate pay from hours worked
- Countdown Timer — measure time intervals
Calculate Hours Now
The free Hours Calculator at RoughTools adds and subtracts multiple time entries, calculates total work hours from clock-in/clock-out times, converts decimal hours to hours:minutes, and computes pay at a given rate. No account needed, completely free.