Time Calculator

Why time doesn’t add like ordinary numbers

Hours and minutes are a base-60 system. Once you go past 59 minutes, the extra spills into the next hour, and that breaks the decimal arithmetic we use every day. The classic mistake is to type times into a calculator with a decimal point:

• Wrong: 7.20 + 1.50 = 8.70, which is not even a valid time.
• Right: 7 h 20 min + 1 h 50 min = 8 h 70 min = 9 h 10 min.

The same trap works in reverse. A timesheet that shows 7.5 hours means 7 hours 30 minutes, because half of 60 is 30. It does not mean 7 hours 50 minutes. When a payroll system or spreadsheet reports decimal hours, convert the fraction by multiplying it by 60: 0.25 h is 15 minutes, 0.75 h is 45 minutes, 0.1 h is 6 minutes.

This time calculator avoids the problem by converting every row to seconds, adding or subtracting them, and only then splitting the total back into hours, minutes and seconds. Minutes over 59 are fine as input: entering 0 hours and 90 minutes counts as 1:30.

Adding and subtracting durations

Use the first mode for anything you need to total: hours spent on a project across several days, the length of a playlist, billable time for a client, or flight segments on a long trip. Each row can be added or subtracted, so you can also work out what is left. For example, if a 40-hour target already has 32:45 logged, enter 40 hours, then subtract 32 hours 45 minutes, and the result is 7:15 still to go.

The total is shown in two forms. h:mm is what people read and write on a timesheet. Decimal hours is what you multiply by an hourly rate. The calculator rounds the h:mm figure to the nearest minute, or to the nearest second when seconds are switched on, and never wraps at 24 hours, so a week of work shows as 42:30 rather than as a time of day.

Using the weekly time card

The second mode is an hours calculator for a work week. For each day, enter the time you clocked in, the time you clocked out and the unpaid break in minutes. The hours worked for that day appear on the right, and the weekly total updates as you type. A typical day from 9:00 to 17:30 with a 30-minute lunch is 8 hours, so five such days make 40:00, or 40 decimal hours.

Night shifts are handled automatically: if the end time is earlier than the start, the shift is counted as ending the next day. A shift from 10:00 PM to 6:30 AM with a 30-minute break comes to 8 hours. Choose “Two weeks” for a biweekly pay period. The overtime threshold is then applied to each week separately.

Overtime and pay estimate

If you enter a number of hours per week in the overtime field, hours above that number are listed as overtime and the rest as regular hours. With an hourly rate, the estimated pay is regular hours × rate plus overtime hours × rate × the multiplier (1.5 by default, editable). For instance, 45 hours at $20 with overtime after 40 gives 40 × 20 + 5 × 20 × 1.5 = $950. This is a plain arithmetic estimate before tax and deductions. It does not apply any specific labor law, so compare it with your pay stub and your employer’s rules.

If you also need to count the calendar days between two dates, for example the length of a contract or a notice period, the date calculator counts days and business days and can add or subtract days from a date.