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Date & Duration Calculator

Base Duration

Duration Set 2

Total Duration

0Years
0Months
0Days
0Hours
0Minutes
0Seconds

Total Duration In:

Days:
0.00
Hours:
0.00
Minutes:
0.00
Seconds:
0.00

Year/Month conversions use average values (365.2425 days/year, 30.436875 days/month).

About This Tool

How to Use

1. Calculate Date Tab:

This tab helps you find a future or past date by adding or subtracting a specific duration from a starting date.

  1. Set Start Date: First, decide if your start date includes a time ('All day: No') or is just the date ('All day: Yes'). Use the input field that appears to select the date (and time, if needed). You can use the built-in picker or type in YYYY-MM-DD or YYYY-MM-DDTHH:mm format.
  2. Enter Duration: In the next section, enter the amount of time (Years, Months, Days, Hours, Minutes, Seconds) you want to add or subtract. Note: Hour, Minute, and Second fields are disabled if 'All day' is 'Yes'.
  3. Calculate: Click the + Add button to add the duration, or the - Subtract button to subtract it.
  4. View Result: The resulting date (and time) appears in the 'Result' box. You get both a standard format (YYYY-MM-DDTHH:mm:ss or YYYY-MM-DD) and a more readable version below it. Click the 'Copy' button next to the standard format result to copy it.

2. Duration Calculator Tab (Default):

This tab lets you add and subtract multiple time durations together to find a total combined duration.

  1. Enter Durations: The calculator starts with two duration sets. Fill in the values (Years, Months, Days, etc.) for the 'Base Duration'. For the second set (and any others you add), first select the operation: Add (+) or Subtract (-), then enter its values.
  2. Add More Sets: Need to combine more durations? Click the + Add Duration Set button below the list on the left. The list will scroll if it gets too long.
  3. View Total Duration: The box on the right, labeled 'Total Duration', automatically calculates the combined total from all sets, considering the Add/Subtract operations. It normalizes the result (e.g., 14 months becomes 1 year & 2 months). You can copy a readable version (like "1 year, 2 months & 10 days") using the small 'Copy' button in this box.
  4. View Totals in Units: Below the main total, you can see the *entire* duration converted into single units (Total Days, Total Hours, etc.). Use the 'Decimal Places' input to adjust the precision. Each unit has its own 'Copy' button.

Who Might Find This Useful?

  • Project Managers: Calculating project end dates based on start dates and estimated durations (days, months).
  • Event Planners: Determining dates for events based on lead times or countdowns.
  • Developers & Testers: Calculating expiry dates, scheduling tasks, or determining time elapsed between events.
  • HR Professionals: Calculating service anniversaries, eligibility periods, or notice periods.
  • Students & Researchers: Finding dates for assignments, experiments, or historical events based on time spans.
  • Anyone tracking deadlines or personal events: Birthdays, anniversaries, warranty expirations, subscription renewals.
  • Anyone needing to sum time intervals: Combining travel times, work logs, or segment durations.

Key Features

  • Two calculation modes: Date + Duration = Date, and Duration +/- Duration = Total Duration.
  • Support for date-only ('All day') and date-time calculations.
  • Ability to add or subtract multiple durations cumulatively.
  • Automatic normalization of duration results (seconds to minutes, months to years, etc.).
  • Display of total duration converted into Days, Hours, Minutes, and Seconds with adjustable decimal precision.
  • Easy copying of results in various formats.
  • Responsive layout for different screen sizes.

A Note on Calculations

  • Date Calculations: Adding/subtracting months and years handles variable month lengths and leap years correctly using JavaScript's Date object logic.
  • Duration Normalization: The primary 'Total Duration' display accurately reflects the sum, normalizing units like seconds, minutes, hours, and months (12 months = 1 year).
  • Total Unit Conversions: The secondary display (Total Days, Hours, etc.) calculates the absolute total time in seconds first. Conversions involving years and months for *this specific display* use average values (approx. 365.2425 days/year, 30.436875 days/month) for simplicity, as noted below that section.
  • Timezones: Date/time inputs are generally interpreted in your browser's local timezone.