JLJosh Liljenquist

Date & time calculator

Time Duration Calculator

Measure the elapsed duration between two complete date-and-time values. The calculation uses civil clock values exactly as entered and does not change because the browser happens to be in another timezone or daylight-saving period.

By

Enter values and select Calculate.

How to use this calculator

  1. Enter complete start and end dates and times.
  2. Calculate to see component and total-unit results.
  3. If the endpoints were entered backward, use Swap and calculate again.
  4. Use Hours Calculator for one simple clock interval or Days Between Dates for a date-only comparison.

Formula and method

Convert each explicit Gregorian date and clock time to a timezone-neutral civil-second index, then subtract start from end and decompose the result.

Worked example

March 1 at 9:00 AM to March 2 at 9:00 AM is exactly 24 hours. No daylight-saving or location offset is applied.

Assumptions and limits

  • This calculator compares the date and time values you enter and does not apply timezone conversions.
  • The Gregorian year range is 1600 through 9999.
  • End must be equal to or later than start.
  • Leap days are included; leap seconds and timezone rules are not modeled.

Understanding the result

The result follows the stated calendar or civil-clock rules rather than guessing a timezone, work policy, holiday calendar, or legal definition. Read the displayed endpoint and start-day policy before using a count in planning or records.

Common mistakes

  • Assuming the result converts between timezones
  • Using a clock-only job that belongs in Hours Calculator
  • Silently taking the absolute value of reversed endpoints
  • Confusing total hours with the remaining hours component

Methodology note

The calculator uses strict ISO-style date components, Gregorian leap-year rules, explicit clock values, and the deterministic policy shown on this page. It does not call a remote calculation, timezone, geolocation, payroll, calendar, or holiday service.

Hours between two clock timesCompare calendar dates onlyConvert Unix timestamps and UTC values

Browse all calculators.

This browser-local utility is a calculation aid, not legal, payroll, scheduling, employment, tax, or official-calendar advice. Confirm the rules that apply to your situation.