Perform time arithmetic with our free Time Calculator. Add or subtract hours and minutes from any start time with automatic day rollover tracking and 100% offline privacy.
Select starting hour, minute, and AM/PM or click 'Use Current Time' to auto-fill system time.
Choose 'Add Time' to shift forward or 'Subtract Time' to shift backward, then set duration hours and minutes.
Instantly view calculated time in 12h or 24h format with automatic day rollover indicators (+1 Day, Next Day).
Your time inputs and schedule adjustments are processed entirely inside your browser using client-side JavaScript. Nothing ever travels over a network to any server — making BunchTool 100% private.
Calculations run locally in real time as you change time selectors, toggle 12h/24h formats, or adjust duration sliders. Results update dynamically without delays.
Uses precise sexagesimal base-60 arithmetic to handle hour/minute carries and multi-day calendar boundaries seamlessly.
Base-60 Sexagesimal Arithmetic: Unlike standard decimal math (base-10), time calculation relies on sexagesimal (base-60) units where 60 seconds equal 1 minute, and 60 minutes equal 1 hour.
The mathematical formulas are:
\(\text{Start Time Minutes: } M_{\text{start}} = (H_{24} \times 60) + M\)
\(\text{Add/Subtract Shift: } M_{\text{final}} = M_{\text{start}} \pm \left( (H_{\text{dur}} \times 60) + M_{\text{dur}} \right)\)
\(\text{Day Offset} = \lfloor \frac{M_{\text{final}}}{1440} \rfloor, \quad \text{Target Time} = M_{\text{final}} \pmod{1440}\)
Day Rollover & Military Time: When adding 3 hours to 11:15 PM, the time crosses the 1440-minute (24-hour) midnight threshold, resulting in 02:15 AM on the next day (+1 Day offset). Switching between 12-hour AM/PM and 24-hour formats allows seamless conversion between civilian clock time and military operational timetables.