Time Calculator: Add or Subtract Hours, Minutes, Seconds

This time calculator adds and subtracts time durations or shifts a specific date and time by a given amount. It operates in two modes: Duration (sum or subtract hours, minutes, and seconds across multiple rows, or type an expression like 1h 30m + 45m) and Add/Subtract from Date (pick a starting datetime and add or subtract days, hours, minutes, and seconds to find the resulting date and time). Carry-over is automatic, 65 minutes becomes 1 hour 5 minutes, 90 seconds becomes 1 minute 30 seconds, following the sexagesimal (base-60) system used in timekeeping. Results include the total duration in hours, minutes, and seconds, plus decimal-hour and total-seconds equivalents for payroll and project tracking. Copy Result exports a human-readable string for emails, spreadsheets, or reports. All calculations run locally in your browser.

Time arithmetic uses the sexagesimal (base-60) system: $60\text{ sec} = 1\text{ min},\quad 60\text{ min} = 1\text{ hour},\quad 24\text{ h} = 1\text{ day}$. When adding durations, the calculator sums each unit (seconds, minutes, hours) independently, then normalizes by carrying excess units upward, if seconds reach 60 or more, a minute is added; if minutes reach 60, an hour is added. For subtraction, the first row is the minuend and subsequent rows are subtrahends; if the result is negative, a "Negative Time Difference" label appears with the absolute magnitude. In Date mode, the calculator converts the start datetime to a timestamp, adds or subtracts the entered span in total seconds, and converts back to a calendar date and time with proper month and year boundaries. Expression mode parses tokens (d, h, m, s) and operators (+ −) left to right, converts everything to seconds internally, then formats back into days, hours, minutes, and seconds.

Choose your mode at the top: Duration for adding or subtracting time values, or Add/Subtract from Date for shifting a specific datetime. In Duration mode, select Rows to enter hours, minutes, and seconds per row, toggle Add (+) to sum all rows or Subtract (−) to take the first row minus the rest, or switch to Expression and type shorthand like 1h 30m + 45m or 2d − 1h 20m using d (days), h (hours), m (minutes), and s (seconds). In Date mode, pick a start date and time with the datetime picker, then enter the days, hours, minutes, and seconds you want to add or subtract. The results panel shows the total duration with automatic carry-over, decimal hours, total minutes, and total seconds. In Date mode, you see the resulting date and time with a day-shift badge when the date changes. Click Copy Result to paste the human-readable output into emails, spreadsheets, or reports.

Choose your mode: Duration (add or subtract time values using rows or an expression), or Add/Subtract from Date (shift a specific datetime). In Duration mode, use Rows to enter hours, minutes, and seconds per row. Add sums all rows, Subtract takes the first row minus the rest, or use Expression for shorthand like 1h 30m + 45m or 2d - 1h 20m. In Date mode, pick a start datetime, then enter days, hours, minutes, and seconds to add or subtract. Copy the result with one click.

Time uses base 60: $60\text{ sec} = 1\text{ min},\quad 60\text{ min} = 1\text{ hour}$. When you add durations, excess units roll up: 65 minutes becomes 1 hour 5 minutes; 90 seconds becomes 1 minute 30 seconds. The calculator normalizes everything internally, you can even enter 2h 65m 90s and get 3h 6m 30s.

In Expression mode, type units with numbers: d for days, h for hours, m for minutes, s for seconds. Combine with + and −. Examples: 1h 30m + 45m → 2h 15m; 2d - 1h 20m → 1 day, 22 hours, 40 minutes. The parser updates as you type.

If you subtract a larger duration from a smaller one (e.g., 1 hour minus 2 hours), the calculator shows "Negative Time Difference" and displays the magnitude with a minus sign. Use the Copy Result button to paste the human-readable string (e.g., "3 Hours, 15 Minutes, 0 Seconds" or "Wednesday, Feb 18, 2026 at 10:05 PM") into emails, spreadsheets, or reports.