Add and subtract time, count the time between two clocks, or shift a date.
Who this is for: Adding durations and counting time across midnight.
Operation
How it is worked out
1First duration in seconds1×86,400 + 2×3,600 + 45×60 + 0 = 96,300 s
2Second duration in seconds0×86,400 + 5×3,600 + 30×60 + 20 = 19,820 s
3Add96,300 + 19,820 = 116,120 s → 1 day 8 hours 15 minutes 20 seconds
Calculated in your browser — the numbers you enter are never sent to our servers.
Add or subtract days, hours, minutes and seconds, find the time between two clock times — even across midnight — add a duration to a date and time, or type a quick expression such as 1d 2h + 45m − 30s. Every result is shown in days, hours, minutes, seconds and decimal hours.
Best for: Adding up durations, Shift lengths, Deadlines and countdowns, Converting to decimal hours
Updated September 2026 · Estimates only, not financial advice.
1 day 2 hours 45 minutes plus 5 hours 30 minutes 20 seconds is 1 day 8 hours 15 minutes 20 seconds
Time does not add like ordinary numbers, because 60 minutes make an hour and 24 hours make a day. The reliable way is to turn everything into one unit, add, and turn it back. The calculator uses seconds, so nothing is ever rounded.
seconds = d × 86,400 + h × 3,600 + m × 60 + s
1 day 2 hours 45 minutes is 86,400 + 7,200 + 2,700 = 96,300 seconds. 5 hours 30 minutes 20 seconds is 18,000 + 1,800 + 20 = 19,820 seconds. Together that is 116,120 seconds: 1 day (86,400), 8 hours (28,800), 15 minutes (900) and 20 seconds. Subtracting instead gives 76,480 seconds, or 21 hours 14 minutes 40 seconds. A result below zero keeps its minus sign rather than wrapping around.
From 10:30 PM to 6:15 AM is 7 hours 45 minutes — the clock wraps past midnight
To find the time between two clock times, subtract the start from the end. 9:15 AM to 5:45 PM is 17:45 − 9:15 = 8 hours 30 minutes, or 8.5 hours in decimal form, which is what payroll and timesheets use.
When the end time is earlier on the clock than the start, the period must run into the next day, so the calculator adds 24 hours before subtracting: 6:15 AM is 22,500 seconds after midnight, 10:30 PM is 81,000, and (22,500 + 86,400) − 81,000 = 27,900 seconds, or 7 hours 45 minutes. Times can be typed in either 12-hour form (6:15 am, 12:00 PM) or 24-hour form (06:15, 22:30); 12:00 AM is midnight and 12:00 PM is noon.
Tuesday 22 September 2026 at 10:00 AM plus 3 days 18 hours is Saturday 26 September at 4:00 AM
Adding a duration to a date moves the clock forward and rolls over into the next day, month or year as needed, including leap days: 28 February 2024 plus one day is 29 February, while 28 February 2023 plus one day is 1 March.
The calculator works on the wall clock. Adding 24 hours always lands on the same clock time the next day, even on a night when clocks change for daylight saving, when the real elapsed time is 23 or 25 hours. For a deadline that has to be exact to the hour across a clock change, check the local rule for that date.
Type 1d 2h 3m 4s + 4h 5s − 2030s and get 1 day 5 hours 29 minutes 19 seconds
Expression mode reads a whole sum at once. Each term is one or more numbers with a unit — w for weeks, d for days, h for hours, m for minutes and s for seconds, or the words themselves — and terms are joined with + or −. The example is 93,784 + 14,405 − 2,030 = 106,159 seconds.
A number without a unit is refused rather than guessed, so "5 + 3" asks you to say whether you mean minutes or hours. In this mode m always means minutes; months are not a fixed length, so they are not a unit.
Why 8 hours 30 minutes is 8.5 hours, not 8.30
Decimal hours divide the minutes by 60: 30 minutes is 0.5 hours, 15 minutes is 0.25, and 45 minutes is 0.75. Writing 8 hours 30 minutes as 8.30 on a timesheet under-pays the half hour, because 8.30 decimal hours is only 8 hours 18 minutes.
Every result here includes the decimal-hours figure. For a week of shifts with breaks and pay, the timesheet calculator totals each day for you.
Worked example
1 day 2 hours 45 minutes plus 5 hours 30 minutes 20 seconds.
Worked example
First duration = 96,300 s
Second duration = 19,820 s
Sum = 116,120 s
Answer = 1 day 8 hours 15 minutes 20 seconds
Limitations
Daylight-saving changes are not applied to date arithmetic.
Months and years are not units here, because their length varies — use the date calculator for those.
Frequently Asked Questions
How do I add hours and minutes?
Turn both into minutes (or seconds), add them, and turn the total back into hours and minutes. 2 h 45 min + 1 h 30 min = 165 + 90 = 255 minutes = 4 h 15 min.
How many hours are there from 10:30 PM to 6:15 AM?
7 hours 45 minutes. Because the end is earlier on the clock, it is the next day: (6:15 + 24:00) − 22:30 = 7:45.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
DaysCount days between two dates, add or subtract days, or count business days excluding weekends and holidays, with a full calendar breakdown.
TimesheetCalculate hours worked across a week, two weeks, or a month from clock-in and clock-out times, with lunch-break deduction, overtime, and an Excel export.
Time ZoneConvert a date and time between EST, IST, GMT, UTC, CET, PST, or any IANA time zone, with live daylight-saving handling and a multi-zone world clock view.
AgeCalculate exact age in years, months, and days from a birth date, with total days lived, day born, a next-birthday countdown, and Excel/SQL/code formula examples.
Time PercentageWork out what percentage one span of time is of another, or the percentage increase or decrease between an old and a new duration.
Time UnitNanoseconds to fortnights exactly, with months as a real calendar range and four different years side by side — because two of those units have no fixed length.
Times are computed live from your browser's built-in time zone database, which relies on your browser and operating system being reasonably up to date. This tool does not model leap seconds. For legal, contractual, travel, or safety-critical timing, confirm the exact local time with an authoritative source.
Published a time calculator from the calculator.net list: add or subtract durations, the time between two clock times across midnight, a duration added to a date and time, and time expressions.
Exact integer-second arithmetic; wall-clock date arithmetic stated plainly (no daylight-saving shift).
Added an automated formula suite with calendar, golden, boundary and round-trip cases.
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