⏰ Time Calculator
Time Add / Subtract
Time Difference — Time Only
Time Difference — With Date
Picking the Right Mode
- Add / Subtract: "3 hours 20 minutes after 14:30 is…?" — known start, projected end. The base field includes a date, so results past midnight roll into the next day automatically.
- Time Only difference: "How long from 14:00 to 16:30?" — two clock times within one day. It refuses an end time earlier than the start, because without dates it can't tell backwards from overnight.
- With Date difference: anything that might cross midnight — shifts, flights, log windows — belongs here, with day totals included.
Rule of thumb: project a moment with Add/Subtract, measure a length with a difference mode — and the instant midnight is involved, use With Date.
Decimal Hours: The Timesheet Trap
Payroll and billing systems usually want decimal hours, but clocks speak hours:minutes — and mixing them up is the most common timesheet error:
- 1.5 hours is 1:30, not 1:50. Convert minutes by dividing by 60: 45 minutes = 0.75 h, so 7:45 = 7.75 hours.
- The reverse: multiply the decimal part by 60. 6.4 hours = 6:24, not 6:40.
- Common billing increments: lawyers bill in 6-minute tenths (0.1 h), many agencies in quarter hours (0.25 h). This tool's "Total Hours" row gives you the decimal figure directly — no mental conversion.
- Adding clock durations: 45 min + 30 min = 75 min = 1:15. Sixty-based carrying is exactly what the Add/Subtract mode automates.
Measuring Durations from Timestamps
The With-Date mode doubles as a log analyzer: paste the start and end timestamps of a deploy, an outage, or a batch job (format YYYY-MM-DD HH:mm:ss) and read the duration in whichever unit you need — seconds for SLA math, decimal hours for reports. A couple of habits that prevent mistakes:
- Make sure both timestamps are in the same time zone before comparing — logs often mix UTC and local time, which silently adds or removes whole hours.
- In DST-observing regions, wall-clock differences across a changeover are off by an hour from real elapsed time; convert to UTC first when it matters.
- For sub-second precision (API latency), this tool's smallest unit is the second — use your profiler for milliseconds.
Frequently Asked Questions
Do the totals reset after 24 hours?
No — total seconds, minutes, and hours are cumulative. A 48-hour span shows 48 in the hours row, not zero. The formatted row at the bottom gives the "X days Y hours Z minutes" breakdown.
Why won't Time-Only mode accept an end before the start?
Without dates the tool can't distinguish "went back 2 hours" from "22 hours overnight." Rather than guess wrong, it asks you to state the dates explicitly in With-Date mode.
Is the time input 12-hour or 24-hour?
24-hour format (14:30, not 2:30 PM) — it's unambiguous and matches log output. If seconds don't matter, enter 00.
Does daylight saving time affect results?
Calculations are pure wall-clock arithmetic. Across a DST changeover, wall-clock difference and physically elapsed time differ by one hour — convert both ends to UTC when measuring real durations across a change.