Time Duration Calculator
Switch between finding the difference between two dates/times and adding or subtracting a duration from a specific date. Everything stays in your local timezone for straightforward planning.
This is a convenience tool for everyday scheduling and planning. For legal or contractual timing, always confirm requirements around business days, time zones, and daylight saving rules.
Choose mode
Difference between two dates/times
Start
End
Result
Enter a start and end date to see the time between them.
When a time duration calculator is actually useful
Time math looks simple until you actually have to do it under pressure. You might be trying to see how long a trip lasted, how many days you have between two deadlines, or what date lands exactly 30 days after a project kickoff. This calculator focuses on those everyday questions: how much time is between A and B, or what does A plus a certain duration look like.
In difference mode, you enter a start and end date (and optionally times) and get a breakdown in days, hours, minutes, and seconds, along with total hours, minutes, and seconds. In add/subtract mode, you pick a base date and tell the tool how many days, hours, minutes, and seconds to move forward or backward. The result is shown with day of week, which makes it easier to reason about things like weekend boundaries or weekday meetings.
Calendar days vs. hours, minutes, and seconds
A calendar day is not just 24 hours on a clock—it is also a specific date on the calendar. For many practical questions, you only care about whole days: how many nights you are renting a place, how many days you have to finish a task, or how many days remain until an event. Other times, the exact time of day matters, such as overlapping shifts, streaming schedules, or timed exams.
This calculator reports both the full day/hour/minute/second breakdown and total hours/minutes/seconds. That way, you can quickly say “this is about three days and four hours” or “roughly 76.2 hours” depending on which is more intuitive for your use case.
Time zones, blank times, and negative durations
Time zones and daylight saving shifts can make cross-border scheduling messy. To keep things predictable, this tool always works in your browser's local timezone and does not attempt to adjust for other zones. Blank time fields are treated as midnight (00:00), which keeps the math simple for tasks like “days until” or “how many days apart”.
If you put the end time before the start time in difference mode, the tool still calculates the length of the gap but marks it as a negative duration. This is handy when you are curious how far in the past or future a date is relative to another anchor, even if the order is reversed.
Examples of where this helps
- Trip planning. Count the exact days and hours between departure and return to estimate costs or recovery time.
- Project timelines. From a kickoff date, add a certain number of days and hours to see realistic handoff points.
- Content and reminders. Pick a base posting date and add or subtract durations to schedule recurring tasks.
For anything involving legal contracts, compliance, or time zones across regions, use this tool only as a rough guide and confirm details with official sources or your legal team. Daylight saving changes and jurisdiction-specific rules can affect exact cutoffs.