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Date & Time

Time Calculator

Add or subtract durations, or find the exact time between two clock readings.

By Nitin Raturi · Last reviewed

Your time inputs

How to use this Time Calculator

Pick a calculation, enter whole time units, then read the exact result.

  1. Choose duration arithmetic or time between clock readings.
  2. For durations, enter parts and add or remove rows; for clock times, enter start and end.
  3. Choose automatic rollover or enter the known day difference.
  4. Read the normalised duration and exact totals in seconds, minutes, hours and days.

Good to know

  • Invalid values show a message and do not replace the last valid calculation.
  • A day is exactly 24 hours here; dates, time zones and daylight-saving changes are not applied.

Calculation mode

Choose whether to combine durations or compare two clock readings.

How to fill it in

  • Use Add / subtract durations for one or more lengths of time.
  • Use Time between clock times for start and end readings on a clock.

Example

The default duration rows total 1 day, 4 hours, 15 minutes, 0 seconds.

Add or subtract

Choose how the duration rows are combined.

How to fill it in

  • Add totals every row.
  • Subtract starts with row 1, then subtracts each later row in order.

Example

Subtracting one hour from two hours gives −0 days, 1 hour, 0 minutes, 0 seconds.

Tip: The result can be negative; its sign is shown separately from the normalised duration.

Duration, row 1

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration, row 2

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Duration parts

Enter one length of time as whole days, hours, minutes and seconds.

How to fill it in

  • Days may be 0 or more. Hours are 0–23; minutes and seconds are 0–59.
  • Use Add a duration to include as many rows as you need.

Example

The default rows add to 1 day, 4 hours, 15 minutes, 0 seconds.

Tip: Each row is converted to integer seconds before the rows are combined.

Your result

Combined duration

1 day, 4 hours, 15 minutes, 0 seconds

Total seconds
101700 s
Total minutes
1695 min
Total hours
113/4 h
Total days
113/96 days

Each day is exactly 24 hours. Fractions are exact and are not rounded.

ChangelogHow we test this calculatorEmbed this calculator

How this calculator works

The default rows total 1 day, 4 hours, 15 minutes, 0 seconds; all arithmetic is done as whole seconds.

  1. Step 1Enter time partsdays · hours · minutes · secondsUse one or more durations or two clock readings.
  2. Step 2Convert to seconds1 day = 86,400 secondsThe same fixed unit makes addition and subtraction direct.
  3. Step 3Read the result1 day, 4 hours, 15 minutes, 0 secondsSee a normalised duration and exact totals in four units.

Each entered duration row uses whole seconds. Hours, minutes and seconds in a row stay within their usual ranges; extra time appears in the normalised result instead.

What this calculation assumes

  • Fixed-length dayA day is exactly 24 hours, or 86,400 seconds, for this calculation.
  • Exact unitsMinute, hour and day totals are exact fractions when seconds do not divide evenly.
  • No calendar rulesDates, time zones, daylight-saving changes and leap seconds are not applied.

Worked example

Add 1 day 2 hours 30 minutes and 1 hour 45 minutes
Convert each row
seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds
Add
total = row 1 + row 2
  • row 1first duration 1 day, 2 hours, 30 minutes
  • row 2second duration 1 hour, 45 minutes
  1. First row86,400 + 7,200 + 1,80095,400 s
  2. Second row3,600 + 2,7006,300 s
  3. Combined duration95,400 + 6,3001,01,700 s

The result is 1 day, 4 hours, 15 minutes, 0 seconds. The equivalent total is 1695 minutes; the fraction stays exact instead of being rounded.

Reading your result

  • Duration arithmetic1 day, 4 hours, 15 minutes, 0 secondsAdd or subtract one or more lengths of time.
  • Clock readings1 hour, 45 minutes, 0 seconds23:30 to 01:15 crosses midnight automatically.
  • Negative result−0 days, 1 hour, 0 minutes, 0 secondsA minus sign means the subtracted rows exceed the first row.
Totals in seconds, minutes, hours and days are exact. A fractional unit is written as a reduced fraction.

For clock times, automatic mode uses the next day only when the end time is earlier than the start. If you know the exact day difference, set it manually; the number is applied literally, including negative values.

Time sums work on hours and minutes. Calendar questions need a tool that knows about days and months.

For hours worked across shifts, use the hours calculator. To count days between dates, try the date difference calculator, or move a date forward with the add or subtract dates calculator.

To compare a time across cities, the time zone converter handles daylight saving.

Common mistakes

  • Mistake: Entering 90 minutes in one row.

    Instead: Enter 1 hour and 30 minutes; row minutes are limited to 59.

  • Mistake: Assuming a same-time clock result means a full day.

    Instead: Automatic mode returns zero when start and end match; set a one-day difference for 24 hours.

  • Mistake: Treating a clock reading as a date-aware timestamp.

    Instead: Use a date/time tool for time zones, daylight-saving changes, dates or calendar-day lengths.

Sources and methodology

The second is the SI unit used for the arithmetic. ISO 8601 provides context for date and time representations; this calculator does not parse ISO strings or do calendar arithmetic. The examples are calculated by the same tested logic as the calculator.

About this calculator

Built by Nitin Raturi, a software engineer. Last reviewed 22 Oct 2026. See the editorial policy for how pages are reviewed. Inputs stay in your browser.

Read how we test our calculators, or browse more everyday tools.

Frequently asked questions

How do I add or subtract time?

Enter each duration as whole days, hours, minutes and seconds. Choose add, or subtract each later row from the first.

What happens when the end time is earlier than the start?

With automatic rollover, the calculator treats the end time as the next day. You can instead enter a signed day difference.

Can the result be negative?

Yes. A minus sign appears before the normalised magnitude, and exact totals retain a negative numerator.

How long is a day in this calculator?

Exactly 24 hours, or 86,400 seconds. Calendar dates, daylight-saving changes and leap seconds are not applied.

Are total minutes rounded?

No. When the seconds do not divide evenly into minutes, the total is displayed as an exact reduced fraction.

Does this calculator understand time zones?

No. It compares clock values only and does not use dates, locations or time zones.

Sources and methodology

The formulas are standard time-value-of-money results. We check every figure against golden values worked out independently, by closed form and by month-by-month simulation; see the methodology.

Written and maintained by Nitin Raturi, a software engineer (about the author). Last reviewed 22 Oct 2026; next review due by . Found an error? Tell us.

Changelog

  • : First release with exact duration arithmetic and clock-time rollover.

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