Time Calculator – Add, Subtract & Convert Hours, Minutes & Seconds
Use our free time calculator to add or subtract hours, minutes, and seconds, find the exact duration between two points in time, and convert between time units all in one place, with instant results and no sign-up required.
This time calculator handles three types of time math: adding or subtracting durations, finding the gap between two specific times, and converting between time units like seconds, minutes, hours, days, and weeks.
Every calculation runs through a seconds-based engine under the hood — so carry-overs between seconds, minutes, and hours are always handled correctly, with no rounding errors.
What You Can Calculate
- Add time: Combine two durations into a single total
- Subtract time: Find what remains after removing one duration from another
- Time difference: Measure the exact gap between a start and end time
- Overnight spans: Handles midnight crossings automatically
- Multi-day ranges: Add optional dates for cross-day calculations
- Unit conversion: Switch between milliseconds, seconds, minutes, hours, days, and weeks
| Hours | Minutes | Seconds |
|---|---|---|
| 1 hr | 60 min | 3,600 sec |
| 2 hr | 120 min | 7,200 sec |
| 3 hr | 180 min | 10,800 sec |
| 4 hr | 240 min | 14,400 sec |
| 5 hr | 300 min | 18,000 sec |
| Unit | Equals |
|---|---|
| 1 Week | 7 days = 168 hours |
| 1 Day | 24 hours = 1,440 minutes |
| 1 Hour | 60 minutes = 3,600 seconds |
| 1 Minute | 60 seconds = 60,000 ms |
| 1 Second | 1,000 milliseconds |
How to Use the Time Calculator
Each of the three tabs focuses on a specific type of time arithmetic. Choose the one that matches what you need, enter your values, and click Calculate Time.
Adding Two Time Durations
Select the Add / Subtract Time tab and choose Add Times. Enter the hours, minutes, and seconds for each duration, then click Calculate. The calculator converts both values to seconds, adds them, and converts the total back into hours, minutes, and seconds — so 2h 45m + 1h 30m correctly produces 4h 15m, with no manual carry-over required.
Example: A film runs 1 hour 52 minutes. The director's cut adds 23 more minutes. Enter 1:52:00 and 0:23:00 — the result is 2:15:00.
Subtracting One Duration from Another
Switch to Subtract Times in the same tab. Enter the longer duration as Duration 1 and the amount to remove as Duration 2. The tool checks that the result is not negative and returns the remaining time in HH:MM:SS format.
Example: A 3-hour recording has a 45-minute segment removed. Enter 3:00:00 and 0:45:00 — the result is 2:15:00.
Finding the Duration Between Two Times
Open the Time Difference tab. Type a start time and an end time in HH:MM format. If the span crosses midnight (for example, 22:00 to 06:00), the calculator automatically adds a day to the end time so the result stays positive. For spans that cross multiple days, add the optional start and end dates.
Example: A road trip starts at 08:15 and ends at 19:40. The duration is 11 hours 25 minutes.
Converting Between Time Units
The Time Conversion tab lets you switch between milliseconds, seconds, minutes, hours, days, and weeks. Enter any value, choose the source unit and the target unit, and click Calculate. The Show Details button reveals conversions into all six units at once.
Example: How many minutes are in 2.5 days? Enter 2.5, select Days → Minutes. The answer is 3,600 minutes.
When People Use a Time Calculator
⏱ Everyday Timing
- Cooking: Add prep time and cook time to know your total kitchen time
- Fitness: Sum multiple training segments — warm-up, sets, cooldown
- Travel: Calculate total trip duration across legs and layovers
- Sleep: Find out exactly how long you slept from bedtime to wake time
- Events: Plan a conference agenda by adding each session's length
🎬 Media & Technical Uses
- Video editing: Add clip durations to check total runtime
- Podcast production: Subtract intro/outro to find net content length
- Game development: Convert milliseconds to seconds for frame timing
- Science & research: Convert observation periods across time units
- Music: Calculate set lengths by adding individual track times
Time Conversion Formulas
| Conversion | Formula | Example |
|---|---|---|
| Hours → Minutes | Minutes = Hours × 60 | 3 hours = 180 minutes |
| Minutes → Seconds | Seconds = Minutes × 60 | 5 minutes = 300 seconds |
| Days → Hours | Hours = Days × 24 | 2 days = 48 hours |
| Weeks → Days | Days = Weeks × 7 | 3 weeks = 21 days |
| Decimal hours → HH:MM | Whole = hours; decimal × 60 = minutes | 3.75 hours = 3 h 45 min |
| Seconds → Milliseconds | Milliseconds = Seconds × 1,000 | 5 seconds = 5,000 ms |
Frequently Asked Questions
💡 Tips for Accurate Time Calculations
- Use 24-hour format to avoid AM/PM ambiguity — enter 14:00 instead of 2:00 PM
- Add dates for overnight spans so the calculator knows which day each time belongs to
- Check the Details view to see your result expressed in multiple units at once
- Convert to seconds first when you need a universal common unit for manual comparisons
- Remember leap seconds are rare — for everyday calculations, 1 minute = exactly 60 seconds
- Milliseconds matter in tech — use the conversion tab when working with API response times or frame rates
⚙️ How the Calculator Works
All three modes share the same core: every time value is converted to seconds first. Addition and subtraction operate on those raw second counts. Time differences use JavaScript Date objects to handle calendar logic — including varying month lengths and leap years when dates are supplied. Unit conversions apply fixed multipliers (1 hour = 3,600 seconds, 1 day = 86,400 seconds, and so on). Results are converted back to the display format only after the arithmetic is complete, which keeps rounding errors out of the final answer.