What Is an Hours Calculator?
An hours calculator finds the difference between a start time and end time, subtracts any unpaid breaks, and converts the result to both hours-and-minutes (h:mm) and decimal format. The decimal format — where 7 hours 30 minutes becomes 7.5 — is what payroll systems actually use when multiplying hours by an hourly rate.
This calculator has three modes: Single Shift for one clock-in/clock-out pair, Weekly Timesheet for entering up to seven days and getting a running total, and Add Time for accumulating multiple time blocks (training sessions, project hours, client calls) into one total.
How to Use This Calculator
- Single Shift — Enter start time, end time, and break minutes. Add an hourly rate to see gross pay. The calculator handles overnight shifts automatically.
- Weekly Timesheet — Enter start/end/break for each day. The total updates on Calculate. Add a rate and overtime threshold (default 40 hrs) to see regular pay, overtime pay, and total.
- Add Time — Enter any number of h:mm pairs and click "Add Up All Times" to sum them. Useful for project billing or tracking scattered daily tasks.
The Formula: How Hours Are Calculated
Decimal Hours — Why Payroll Uses Them
Payroll software doesn't multiply by "8 hours 30 minutes" — it multiplies by 8.50. Converting minutes to decimals is the step that bridges a time clock and a paycheck. Quarter-hour rounding (to the nearest 0.25) is common under the FLSA, though exact-minute tracking is more accurate for employees:
| Time (h:mm) | Exact Decimal | Rounded (0.25 increment) | Difference at $20/hr |
|---|---|---|---|
| 0h 15m | 0.25 | 0.25 | $0.00 |
| 0h 30m | 0.50 | 0.50 | $0.00 |
| 0h 45m | 0.75 | 0.75 | $0.00 |
| 1h 00m | 1.00 | 1.00 | $0.00 |
| 7h 30m | 7.50 | 7.50 | $0.00 |
| 8h 00m | 8.00 | 8.00 | $0.00 |
| 8h 20m | 8.333 | 8.25 or 8.50* | $0.83–$1.67 |
| 8h 45m | 8.75 | 8.75 | $0.00 |
*8 hours 20 minutes falls between the 0.25-hr marks. Under FLSA, rounding must be neutral — it can't consistently favor the employer. Many employers now use exact-minute tracking to avoid disputes. This calculator always uses exact minutes, never rounded.
Reference: DOL Fact Sheet #53 — FLSA Timekeeping Requirements
Overtime Rules Under the FLSA
Federal law in the US requires overtime pay (at least 1.5× the regular rate) for non-exempt employees who work more than 40 hours in a workweek. Some states have stricter rules — California, for example, requires daily overtime after 8 hours in a single day, and double time after 12 hours. The federal FLSA threshold is purely weekly:
| Hours Worked | Pay Rule (Federal FLSA) | Example at $20/hr |
|---|---|---|
| 0–40 hrs/week | Regular rate (1×) | 40 × $20 = $800 |
| 41–45 hrs (5 OT hrs) | 1.5× for OT portion | $800 + 5 × $30 = $950 |
| 40 hrs (example above) | Regular rate | 40 × $20 = $800 |
Reference: US Department of Labor — Overtime Pay
Weekly Timesheet — Worked Example
Here's a realistic 6-day schedule with varying hours and breaks. Every row is individually calculated using the same formula as the live calculator above:
| Day | Start | End | Break | Net Hours | Decimal |
|---|---|---|---|---|---|
| Monday | 9:00 AM | 5:30 PM | 30 min | 8h 00m | 8.00 |
| Tuesday | 9:00 AM | 6:00 PM | 30 min | 8h 30m | 8.50 |
| Wednesday | 8:30 AM | 5:00 PM | 30 min | 8h 00m | 8.00 |
| Thursday | 9:00 AM | 5:00 PM | 0 min | 8h 00m | 8.00 |
| Friday | 9:00 AM | 4:30 PM | 30 min | 7h 00m | 7.00 |
| Saturday | 10:00 AM | 2:00 PM | 0 min | 4h 00m | 4.00 |
| Total | 43h 30m | 43.50 |
At $18/hr with a 40-hour OT threshold: regular pay = 40 × $18 = $720.00, overtime = 3.5 hrs × $27 = $94.50, total = $814.50 gross (before deductions). The 3.5 OT hours come from 43.50 − 40 = 3.50.
Night Shifts and Crossing Midnight
When a shift starts in the evening and ends the next morning, the end time is numerically smaller than the start time — which would give a negative result without adjustment. The fix is adding 24 hours (1,440 minutes) to the end time whenever end < start:
5 Tips for Accurate Time Tracking
- Always enter break time separately — never subtract it from your clock-out. Clocking out 30 minutes early to compensate for a break inflates your start or end time and makes your daily records inconsistent. Enter the real clock-out and enter the break separately. For the 9:00 AM–5:30 PM example with a 30-minute break: gross is 8h 30m, net is 8h 00m (8.00 decimal hours). The difference matters at $18/hr — 0.5 hour = $9.00 per day, $45 per week.
- 40 hours per week = 2,080 hours per year — which is why annual salary ÷ 2,080 gives your effective hourly rate. A $52,000 salary works out to $25.00/hr. Tracking your actual hours against this benchmark shows whether you're working your contracted load or consistently over it.
- Use decimal hours for invoicing, not h:mm. When sending a client invoice for "7:45 of consulting," they'll calculate 7.45 hours × your rate — which is wrong. 7h 45m = 7.75 decimal hours. Always convert to decimal before multiplying by your rate: 7.75 × $150/hr = $1,162.50, not 7.45 × $150 = $1,117.50 (a $45 error per invoice).
- For overtime purposes, the workweek is a fixed 7-day period — not rolling. Under the FLSA, your employer defines a specific start day for the workweek (often Sunday or Monday). Hours don't carry over between workweeks — 38 hours one week and 42 the next means 2 hours of OT in week two, not zero OT averaged across both weeks. Source: DOL FLSA Overview
- Track unpaid break time consistently. A 30-minute lunch break deducted every day adds up to 2.5 hours per week, 130 hours per year. At $18/hr, that's $2,340/year in deductions. If your employer requires you to remain on-call during lunch, that time may be compensable under the FLSA — the break must be truly free from work duties to be unpaid.