Time to Decimal Calculator
Convert time between HH:MM:SS and decimal hours.
Perfect for timesheets, payroll, and work hours.
Also converts decimal back to hours and minutes.
What decimal hours actually are
Decimal hours express time as a single number: 7 hours 30 minutes = 7.5, 7 hours 45 minutes = 7.75. The point is that decimal numbers add, subtract, and multiply cleanly. Hours and minutes don’t — 2 hours 50 minutes plus 1 hour 30 minutes is 4 hours 20 minutes, but a calculator naively summing “2.50 + 1.30” gives you 3.80, which is wrong.
That mismatch is why payroll systems, contractor invoicing, time-tracking apps (Toggl, Harvest, Clockify), and accounting software internally use decimal hours even when they display HH:MM to the user.
The conversion formulas
Time → decimal: decimal hours = hours + (minutes ÷ 60) + (seconds ÷ 3600)
So 7:45:30 = 7 + (45 ÷ 60) + (30 ÷ 3600) = 7 + 0.75 + 0.00833 = 7.7583 hours.
Decimal → time:
- hours = floor(decimal hours)
- minutes = floor((decimal hours − hours) × 60)
- seconds = round(((decimal hours − hours) × 60 − minutes) × 60)
7.75 decimal hours = 7 hours, 0.75 × 60 = 45 minutes, 0 seconds → 7:45. 7.7583 decimal hours = 7 hours, 45 minutes, 30 seconds → 7:45:30.
The quarter-hour shortcut everyone in payroll knows
These four conversions cover 95% of timesheet entries:
| Minutes | Decimal |
|---|---|
| :00 | .00 |
| :15 | .25 |
| :30 | .50 |
| :45 | .75 |
Memorising the 15-minute quarters alone handles most timesheet rounding. Many payroll departments round to the nearest 15-minute mark anyway, so workers entering 8:13 typically get logged as 8:15 or 8.25 decimal hours.
Full conversion table (every 5 minutes)
| Time | Decimal | Time | Decimal |
|---|---|---|---|
| 0:05 | 0.083 | 0:35 | 0.583 |
| 0:10 | 0.167 | 0:40 | 0.667 |
| 0:15 | 0.250 | 0:45 | 0.750 |
| 0:20 | 0.333 | 0:50 | 0.833 |
| 0:25 | 0.417 | 0:55 | 0.917 |
| 0:30 | 0.500 | 1:00 | 1.000 |
The minutes column over 60 = decimal value pattern is exact. Half of 60 minutes is 30 — that’s 0.5. A third (20) is 0.333. Two-thirds (40) is 0.667. Three-quarters (45) is 0.75.
Common payroll rounding methods
Federal law (FLSA) allows employers to round time entries — but only if it doesn’t systematically shortchange workers. The three legal methods:
- Quarter-hour rounding (the 7/8 rule). Times in the first 7 minutes round down; 8 minutes or more round up. So 8:07 logs as 8:00, but 8:08 logs as 8:15.
- 6-minute rounding. Each 6-minute increment (tenths of an hour). 8:03 to 8:08 logs as 8:06.
- 1-minute rounding. Exact to the minute. Most accurate, used by modern time-tracking software.
Companies still using quarter-hour rounding from old systems sometimes get sued for systematic under-counting — workers who consistently clock in at :07 and clock out at :53 lose 14 paid minutes a day under that rounding.
Why this matters for hourly workers
A $20/hour worker putting in 7:45 (7.75 decimal hours) earns $155.00. The same worker at 7:30 (7.50 decimal) earns $150.00. A 15-minute rounding error over 250 working days costs $1,250/year — not trivial.
Track time honestly with a tool like Toggl or your employer’s official app. Manual entries that round generously toward the company’s benefit add up to real money over a career.
The 24-hour decimal
For a full workday (less than 24 hours), decimal goes from 0.0 to 23.999…. Beyond 24 hours, you typically either reset (using “elapsed time” not “clock time”) or use formats like “1 day, 6.5 hours”. Excel can be tricky here — the function TIME(25,0,0) returns 1:00 (the next day) rather than 25:00. To display elapsed time beyond 24 hours, format the cell as [h]:mm:ss (square brackets are critical) or just use decimal hours.
Where this trips people up
- Lunch break deductions. A worker clocking in at 8:00, taking lunch from 12:00 to 12:30, and clocking out at 5:00 worked 8.5 hours, not 9.0. Decimal subtraction: 5.00 + 12.00 - 8.00 - 0.50 = 8.50.
- Pay period totals. Adding individual day totals as decimal (8.25 + 7.75 + 8.50 + 7.00 + 8.25 = 39.75) is exact. Adding in HH:MM format (“8:15 + 7:45…”) requires carrying, which is error-prone.
- Overtime thresholds. US federal OT triggers above 40 hours/week. Decimal makes this trivial; HH:MM addition obscures it.
The opposite problem: minutes from a calculator
If you have a decimal value from a calculator (say, 2.3 hours of overtime) and need to express it in HH:MM, multiply the decimal part by 60: 0.3 × 60 = 18 minutes. So 2.3 hours = 2 hours 18 minutes, written as 2:18.
One trap: leading zeros
5 minutes is 0:05, not 0:5. When typing time into a spreadsheet, the leading zero matters — “0:5” reads as 0 hours and 5/100ths (probably parsed as 5 seconds or rejected entirely depending on the software). Always type the full HH:MM with leading zeros on minutes under 10.