Durations use a mixed base – 60 seconds, 60 minutes, 24 hours – so adding them by hand needs carrying at each step. Converting both to seconds, adding, then splitting back avoids errors.
How to use the Time Calculator – Add and Subtract Durations
- Duration 1 – days
- Duration 1 – hours
- Duration 1 – minutes
- Duration 1 – seconds
- Operation
- Duration 2 – days
- Duration 2 – hours
- Duration 2 – minutes
- Duration 2 – seconds
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter the two durations and choose add or subtract.
Tips
- Check whether the end date should be included – event durations usually include it, elapsed time does not.
- Months have 28–31 days, so “one month” is counted by calendar date, not as 30 days.
- Use 24-hour time or set AM/PM carefully when entering clock times.
- Time zones and daylight-saving changes are not applied unless the calculator says so.
Common mistakes to avoid
- Counting a 30-day month when a calendar month is meant (or the reverse).
- Forgetting leap years when counting days across February.
- Mixing decimal hours (7.5 h) with clock time (7:30).
Inputs explained
| Field | What to enter |
|---|---|
| Duration 1 – days | A number |
| Duration 1 – hours | A number |
| Duration 1 – minutes | A number |
| Duration 1 – seconds | A number |
| Operation | Choose one: Add (+), Subtract (−) |
| Duration 2 – days | A number |
| Duration 2 – hours | A number |
| Duration 2 – minutes | A number |
| Duration 2 – seconds | A number |
What each result means
- Total seconds = ([Duration 1 – days]×86400 + [Duration 1 – hours]×3600 + [Duration 1 – minutes]×60 + [Duration 1 – seconds]) + [Operation]×([Duration 2 – days]×86400 + [Duration 2 – hours]×3600 + [Duration 2 – minutes]×60 + [Duration 2 – seconds])
- Days = sign([Total seconds])×floor([Absolute seconds]÷86400)
- Hours = sign([Total seconds])×floor(mod([Absolute seconds], 86400)÷3600)
- Minutes = sign([Total seconds])×floor(mod([Absolute seconds], 3600)÷60)
- Seconds = sign([Total seconds])×mod([Absolute seconds], 60)
- Total hours = [Total seconds]÷3600
- Total minutes = [Total seconds]÷60
Example values
How the main result changes when Duration 1 – days changes and everything else stays at the example values above:
| Duration 1 – days | Days |
|---|---|
| 0.5 | 1 |
| 0.75 | 1 |
| 1 | 2 |
| 1.25 | 2 |
| 1.5 | 2 |
| 2 | 3 |
Formula
Total seconds = (d₁ × 86,400 + h₁ × 3,600 + m₁ × 60 + s₁) ± (d₂ × 86,400 + h₂ × 3,600 + m₂ × 60 + s₂)Then split back into days, hours, minutes and secondsWorked example
Inputs — Duration 1 – days: 1; Duration 1 – hours: 14; Duration 1 – minutes: 35; Duration 1 – seconds: 50; Operation: Add (+); Duration 2 – days: 0; Duration 2 – hours: 10; Duration 2 – minutes: 40; Duration 2 – seconds: 25.
Results — Total seconds = 177,375; Days = 2; Hours = 1; Minutes = 16; Seconds = 15; Total hours = 49.271; Total minutes = 2,956.25.
Frequently asked questions
How do I add times together?
Add seconds, minutes, hours and days separately, carrying 60 seconds to a minute, 60 minutes to an hour and 24 hours to a day.
What is 1 d 14:35:50 + 10:40:25?
2 days 1 h 16 min 15 s.
How many seconds in a day?
86,400.
What formula does the Time Calculator – Add and Subtract Durations use?
Total seconds = (d₁ × 86,400 + h₁ × 3,600 + m₁ × 60 + s₁) ± (d₂ × 86,400 + h₂ × 3,600 + m₂ × 60 + s₂).