A time card is a record of an employee’s working hours — when they clocked in, when they clocked out, how long they were on break, and the total hours worked. Calculating those hours correctly determines the right pay, the right overtime, and the right invoice total.
This guide covers the exact formula for calculating hours from a time card, how to handle breaks and overtime, how to convert time to decimal for pay calculations, and why teams using Slack are skipping the manual calculation entirely.
How to calculate hours worked from a time card
Calculating hours worked from a time card requires three pieces of information: the clock-in time, the clock-out time, and the total break time. The result is the net hours worked — the time that counts toward pay and overtime.
The basic principle is straightforward: subtract the start time from the end time, then subtract any unpaid break time. What makes this slightly more complex in practice is that time is not a decimal system — there are 60 minutes in an hour, not 100 — which means converting to decimal is a necessary step before any pay calculation.
The time card formula — step by step
Step 1: Convert clock-in and clock-out times to minutes from midnight
Multiply the hours by 60 and add the minutes. This converts both times to a common unit.
Clock in at 8:30am: 8 × 60 + 30 = 510 minutes from midnight. Clock out at 5:45pm: 17 × 60 + 45 = 1,065 minutes from midnight.
Step 2: Subtract clock-in from clock-out
1,065 − 510 = 555 minutes worked (before breaks).
Step 3: Subtract unpaid break time
If the employee took a 45-minute unpaid lunch break: 555 − 45 = 510 minutes net working time.
Step 4: Convert back to hours and minutes
510 ÷ 60 = 8 hours, with 30 minutes remaining. Total: 8 hours 30 minutes worked.
A complete example:
An employee clocks in at 9:00am and clocks out at 6:15pm, with a 30-minute unpaid lunch break.
Clock-in: 9 × 60 + 0 = 540 minutes. Clock-out: 18 × 60 + 15 = 1,095 minutes. Gross time: 1,095 − 540 = 555 minutes. Net time: 555 − 30 = 525 minutes. Hours worked: 525 ÷ 60 = 8 hours 45 minutes.
Converting time to decimal hours
Payroll and billing systems typically require decimal hours rather than hours-and-minutes format. The conversion is simple: divide the minutes by 60 and add to the hours.
8 hours 30 minutes: 8 + (30 ÷ 60) = 8.50 hours. 8 hours 45 minutes: 8 + (45 ÷ 60) = 8.75 hours. 7 hours 20 minutes: 7 + (20 ÷ 60) = 7.33 hours. 6 hours 15 minutes: 6 + (15 ÷ 60) = 6.25 hours.
The decimal format is what you multiply by the hourly rate to get gross pay. An employee who worked 8.75 hours at $22/hour earned $192.50 for the day.
Converting decimal back to hours and minutes:
Multiply the decimal portion by 60. 8.75 hours: 0.75 × 60 = 45 minutes → 8 hours 45 minutes.
How to calculate overtime on a time card
Overtime rules vary by jurisdiction and contract, but the two most common frameworks are weekly overtime and daily overtime.
Weekly overtime (US federal standard under FLSA)
Any non-exempt employee who works more than 40 hours in a workweek is entitled to overtime pay at a minimum of 1.5 times their regular hourly rate for those additional hours. The calculation applies to the week as a whole, not day by day.
An employee who works 43 hours in a week at $20/hour: Regular pay: 40 hours × $20 = $800. Overtime: 3 hours × ($20 × 1.5) = 3 × $30 = $90. Total gross pay: $890.
Daily overtime (California and some other states)
Some jurisdictions calculate overtime on a daily basis — typically at 1.5× for hours over 8 in a day, and 2× for hours over 12 in a day. California also applies 1.5× on the seventh consecutive day of work.
An employee in California who works 10 hours in a day at $20/hour: Regular pay: 8 hours × $20 = $160. Overtime: 2 hours × $30 = $60. Total: $220.
Double time
Some contracts and jurisdictions apply double time (2× the regular rate) for overtime beyond a threshold — typically over 12 hours in a day or for work on statutory holidays. Check the employment contract and local labour law for the applicable rates.
How to calculate pay from a time card
Pay calculation from a time card requires three inputs: total regular hours worked, total overtime hours worked (if any), and the hourly rate.
Regular pay: Regular hours × hourly rate. Example: 40 hours × $18 = $720.
Overtime pay: Overtime hours × (hourly rate × overtime multiplier). Example: 5 hours × ($18 × 1.5) = 5 × $27 = $135.
Gross pay: Regular pay + overtime pay. Example: $720 + $135 = $855 gross for the week.
Note on gross vs net pay:
Time card calculations produce gross pay — pay before deductions. Net pay (take-home pay) requires subtracting income tax withholding, Social Security and Medicare contributions (US), pension contributions, health insurance premiums, and any other deductions specified in the employment contract. Payroll software handles these deductions; the time card calculation establishes the gross figure they start from.
Weekly time card calculation
A weekly time card consolidates daily entries into a weekly total. The process is the same as the daily calculation, repeated for each day and summed.
Step 1: Calculate net hours worked for each day using the formula above.
Step 2: Sum the daily totals to get the weekly total in minutes.
Step 3: Convert the weekly total to decimal hours.
Step 4: Identify regular hours (up to 40) and overtime hours (above 40).
Step 5: Apply the appropriate rates to each to calculate gross pay.
For a five-day week with the following hours: Monday 8.5h, Tuesday 9h, Wednesday 8h, Thursday 8.75h, Friday 7.5h — the weekly total is 41.75 hours. Regular pay covers 40 hours; overtime covers 1.75 hours at the premium rate.
Common time card calculation mistakes
Forgetting to convert to a 24-hour clock
Entering 5:30 instead of 17:30 for a 5:30pm clock-out produces a negative result (5:30 minus 9:00 = negative time). Always convert afternoon times to 24-hour format before calculating, or explicitly note am/pm.
Rounding breaks incorrectly
A 47-minute break rounded to 30 minutes inflates the hours worked by 17 minutes. Per employee, per day, this compounds into significant payroll error over time. Log actual break duration rather than rounding to the nearest standard interval.
Ignoring carry-over minutes
Adding hours and minutes by treating them like decimal numbers produces errors. 7h 45m + 6h 30m is not 13h 75m — it is 14h 15m (because 75 minutes = 1 hour 15 minutes). Convert to minutes, add, then convert back.
Not accounting for overnight shifts
An employee who clocks in at 11:00pm and clocks out at 7:00am worked 8 hours, but the raw subtraction (7 − 23 in 24-hour format) gives a negative number. Add 24 hours to the clock-out time when the shift crosses midnight: (7 + 24) × 60 = 1,860 minutes, minus 11 × 60 = 660 minutes = 1,200 minutes = 8 hours.
Applying the wrong overtime threshold
Using a 40-hour weekly threshold in a jurisdiction that applies daily overtime produces incorrect pay. Always check whether the applicable rule is weekly, daily, or both.
How Time Bot replaces the time card in Slack
The manual time card calculation process — log hours, calculate totals, convert to decimal, apply overtime, generate invoice — takes time every pay period and produces data that is only as accurate as the original entries. For teams using Slack, Time Bot removes the manual step entirely.
Time is logged with a single command in any Slack channel:
Starting a task: /t writing client proposal
Switching tasks: /t code review — sprint 14 (the previous task closes automatically)
Taking a break: /t break
Ending the day: /t finish
The result is a complete, timestamped record of every task, every transition, and every break — accurate to the minute, organised by project (Slack channel), and delivered in a daily email report to managers without anyone filling in a time card.
For pay and billing, the data is already in the format needed. Time Bot generates PDF invoices directly from the logged time — selecting the client (channel), the date range, and the hourly rate produces a line-itemised invoice without any manual calculation. The hours are already decimal, the totals are already correct, and the task descriptions are already there.
For compliance with working hour regulations — including the EU Working Time Directive’s requirement for accurate daily records — the timestamped log satisfies the documentation requirement and is exportable to CSV for payroll providers.
Add Time Bot to Slack — 7-day free trial →
FAQ
How do I calculate hours worked from a time card? Subtract the clock-in time from the clock-out time, then subtract unpaid break time. The easiest method is to convert both times to minutes from midnight (hours × 60 + minutes), subtract, subtract break minutes, then convert back to hours and minutes. To get decimal hours for pay calculations, divide the remaining minutes by 60 and add to the hours.
How do I convert time card hours to decimal? Divide the minutes portion by 60 and add it to the hours. 7 hours 30 minutes = 7 + (30 ÷ 60) = 7.5 hours. 8 hours 45 minutes = 8 + (45 ÷ 60) = 8.75 hours. 6 hours 20 minutes = 6 + (20 ÷ 60) = 6.33 hours. Multiply the decimal result by the hourly rate to get gross pay.
How is overtime calculated on a time card? Under US federal law (FLSA), overtime applies to non-exempt employees who work more than 40 hours in a workweek, at a minimum of 1.5 times the regular hourly rate. Some states apply daily overtime (over 8 hours in a day). To calculate: identify total hours worked, split into regular (up to 40) and overtime (above 40), multiply each by the appropriate rate, and sum.
What is the difference between gross pay and net pay on a time card? A time card calculation produces gross pay — the total earnings before deductions. Net pay (take-home pay) is gross pay minus income tax withholding, Social Security and Medicare contributions, pension, health insurance, and any other applicable deductions. The time card establishes the gross figure; payroll software applies the deductions.
How do I calculate overnight shift hours on a time card? Add 24 hours to the clock-out time when the shift crosses midnight, then subtract the clock-in time. An employee who clocks in at 11:00pm and clocks out at 7:00am: (7 + 24 = 31:00) minus 23:00 = 8 hours. In minutes: (31 × 60) − (23 × 60) = 1,860 − 1,380 = 480 minutes = 8 hours.
What is a free time card calculator? A free time card calculator is a tool that computes total hours worked from clock-in and clock-out times, accounting for breaks and overtime, without requiring payment or sign-up. This article covers the manual calculation method — the same arithmetic any time card calculator performs — so you can verify results or calculate without a tool.
