About

Managing life around non-standard work hours requires precision. Shift workers often struggle to predict whether a specific date months in the future falls on a work day or a rest day. Traditional calendar apps assume a weekly 5-2 cycle, failing to accommodate complex rotations like the Panama schedule, DuPont shift, or simple 4-on-4-off patterns. This tool solves the planning gap by projecting custom cyclic patterns onto a standard Gregorian calendar.

Accuracy in forward planning prevents scheduling conflicts for medical appointments, family events, or vacations. By defining a specific rotation sequence and a reference start date, the system uses modular arithmetic to mathematically determine the status of any future date. This allows for long-term visualization without the need for manual entry of repeating events.

Formulas

The core logic uses modular arithmetic to map linear time to a repeating cycle. The position P within the cycle for any given target date D_target is calculated relative to a reference start date D_start.

P = (D_target − D_start) × mod L

Where L is the total length of the shift pattern sequence. If the result is negative (backward projection), adjustments are made to align with the cycle modulus. The specific shift type assigned to the date corresponds to the element at index P in the defined pattern array.

Reference Data

Pattern Name	Cycle Length (Days)	Description	Typical Rotation
Panama (2-2-3)	14	Slow rotation allows for every other weekend off.	2 On, 2 Off, 3 On, 2 Off, 2 On, 3 Off
DuPont	28	Includes a 7-day break but requires 12-hour shifts.	4 Nights, 3 Off, 3 Days, 1 Off, 3 Nights, 3 Off, 4 Days, 7 Off
4 On, 4 Off	8	Consistent ratio, rotates through all days of the week.	4 Days (12h), 4 Days Off
Pitman (Fixed)	14	Fixed days, employees work the same days every two weeks.	2 On, 2 Off, 3 On, 2 Off, 2 On, 3 Off
Continental	7	Fast rotation, changes shifts weekly.	2 Days, 2 Swings, 3 Nights, 2 Off, 2 Days, 3 Swings, 2 Nights, 3 Off
Kelly Schedule	9	Used often by firefighters. 24-hour shifts.	1 On, 1 Off, 1 On, 1 Off, 1 On, 4 Off
5-5-4	14	Common in law enforcement.	5 On, 5 Off, 4 On, 4 Off
Standard 5-2	7	Typical office schedule.	5 Days Work, 2 Days Off
9/80 Schedule	14	80 hours in 9 days.	9 Days On (various hours), 1 Day Off every 2 weeks

Frequently Asked Questions

The tool uses standard Date object logic which automatically accounts for leap years. A 4-on-4-off pattern will simply continue its mathematical sequence across February 29th, maintaining the correct rhythm without manual intervention.

Yes. After generating the schedule, use the "Export iCal" button. This creates a .ics file that can be imported into Google Calendar, Apple Calendar, or Outlook. It creates all-day events for your work shifts.

This tool projects a single continuous pattern. If your rotation changes (e.g., moving from Day Shift to Night Shift permanently), you should generate a schedule up to the change date, and then run a separate generation for the new pattern starting from that date.

The start date anchors the calculation. If you work a "2 days on, 2 days off" pattern, the tool needs to know if today is Day 1 or Day 2 of that sequence. Always pick a date where you know exactly where you are in the rotation (e.g., the first day of your last "Day Shift" block).