Time Calculator – Add, Subtract & Convert Hours, Minutes & Seconds
Add or subtract durations, find the exact time between two events, convert between time units, or calculate multi-step expressions all in one free tool, with instant results and no sign-up needed.
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Hours can be any whole number. Minutes and seconds must be 0–59.
Enter values and click Calculate Time
This time calculator handles four types of time math in one place adding durations, subtracting them, measuring the gap between two clock times, converting between time units, and evaluating multi-step expressions.
All calculations run through a seconds-based engine, so carry-overs between seconds, minutes, and hours are always exact no rounding errors.
- Add time: Combine two durations
- Subtract time: Find what remains
- Time difference: Exact gap between two clock times
- Overnight spans: Midnight crossings handled automatically
- Multi-day ranges: Add optional dates
- Unit conversion: ms → sec → min → hr → days → weeks
- Expression mode: Chain multiple additions and subtractions in one line
| Unit | Equals |
|---|---|
| 1 week | 7 days / 168 hours |
| 1 day | 24 hours / 1,440 min |
| 1 hour | 60 min / 3,600 sec |
| 1 minute | 60 seconds / 60,000 ms |
| 1 second | 1,000 milliseconds |
| Hours | Minutes | Seconds |
|---|---|---|
| 1 hr | 60 | 3,600 |
| 2 hr | 120 | 7,200 |
| 4 hr | 240 | 14,400 |
| 8 hr | 480 | 28,800 |
| 12 hr | 720 | 43,200 |
| 24 hr | 1,440 | 86,400 |
Click any example to load it.
How to Use the Time Calculator
The calculator has four tabs, each targeting a different type of time problem. Choose the tab that matches your task, fill in the values, and click Calculate Time. Results appear instantly. Use Show All Units to expand the output into hours, minutes, seconds, days, and weeks at once.
Adding Two Time Durations
Open the Add / Subtract tab, choose Add Times, and enter hours, minutes, and seconds for each duration. The tool converts both to seconds, adds them, and converts the total back so 2h 45m + 1h 30m correctly returns 4h 15m without any manual carry-over.
Subtracting One Duration from Another
Switch to Subtract Times in the same tab. Enter the longer duration as Duration 1. The calculator checks that the result cannot be negative and returns the remaining time in HH:MM:SS format.
Finding the Duration Between Two Times
Use the Time Difference tab. Enter a start time and an end time in HH:MM. For overnight spans (22:00 to 06:00), the calculator automatically adds a day to the end time. For multi-day spans, add the optional start and end dates.
Converting Between Time Units
The Convert Units tab switches between milliseconds, seconds, minutes, hours, days, and weeks. Enter a value, pick the source and target unit, and click Calculate. Show All Units reveals the result in every unit simultaneously.
Expression Mode Multi-Step Calculations
The Expression tab lets you type a full time calculation in plain text. Use d, h, m, s after each number and chain them with + or -.
When People Use a Time Calculator
Everyday Timing
- Cooking: Total prep time + cook time
- Fitness: Sum warm-up, sets, and cooldown
- Travel: Total trip duration across legs and layovers
- Sleep tracking: Exact hours from bedtime to wake time
- Event planning: Add each session's length for an agenda
Media & Technical Uses
- Video editing: Add clip lengths to check total runtime
- Podcast production: Subtract intro/outro for net content length
- Game development: Convert milliseconds for frame timing
- Science: Convert observation periods across units
- Music: Calculate set length by adding 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 number = hours; decimal × 60 = minutes | 3.75 hours = 3h 45m |
| Seconds → Milliseconds | ms = Seconds × 1,000 | 5 seconds = 5,000 ms |
| Hours → Seconds | Seconds = Hours × 3,600 | 2 hours = 7,200 seconds |
| Days → Seconds | Seconds = Days × 86,400 | 1 day = 86,400 seconds |
Common Mistakes to Avoid
Entering minutes above 59
Minutes and seconds must be 0–59. If you have 90 minutes, enter 1 hour 30 minutes instead.
Forgetting dates on overnight spans
For spans that cross multiple days, add both start and end dates. The midnight auto-detection only works for single-night crossings without dates.
Mixing AM/PM and 24-hour format
The time difference tab uses the browser's native time input, which defaults to your system format. Use 14:00 for 2:00 PM to avoid ambiguity.
Subtracting a longer duration from a shorter one
The calculator blocks negative results. If you get an error, check which duration is larger and swap them.
Confusing duration with clock time
The Add/Subtract tab works with durations (how long). The Time Difference tab works with clock times (what time). Use the right tab for your task.
Tips for Accurate Results
- Use 24-hour format to remove AM/PM ambiguity
- Add dates for any span that crosses midnight or spans multiple days
- Use Show All Units to see your result expressed in every unit at once
- Use Expression Mode for complex multi-step problems faster than clicking through tabs
- Milliseconds matter in software use the conversion tab for API response times or frame rates
How the Calculator Works
Every time value is converted to a whole number of seconds before any arithmetic takes place. For the Time Difference tab, native JavaScript Date objects handle calendar logic including varying month lengths and leap years when dates are provided. Unit conversions use fixed multipliers (1 hour = 3,600 seconds; 1 day = 86,400 seconds). Results are converted back to HH:MM:SS only after the arithmetic is complete, keeping rounding errors out of the final answer. Expression mode tokenises the input string into signed second values and sums them in a single pass.
Frequently Asked Questions
Calculate Any Time Value Instantly
Whether you need to add a few durations, measure an elapsed span, or chain a complex multi-step expression, this free time calculator gives you the answer immediately. All four modes add/subtract, time difference, unit conversion, and expression — work in your browser with no login or installation required. Results are accurate to the second and ready to expand into any time unit with one click.