About

For professionals in emergency services, fire departments, and security sectors, the standard Monday-to-Friday calendar is virtually useless. Working on a "Day On, Three Off" (1/3) schedule requires a specialized tool to visualize long-term planning. Accuracy in this schedule is critical; missing a shift due to calendar confusion can lead to disciplinary actions, while miscalculating a rest day can ruin planned family vacations or medical appointments.

This tool solves the chaos of rotating rosters. By defining a single "Anchor Date" (a known working shift), the system mathematically projects your schedule across the entire year of 2026. It is designed specifically for the 24-hour shift cycle followed by 72 hours of recovery, allowing personnel to instantly see if a specific future date falls on a "Guard" (duty) day or a recovery day.

Formulas

The underlying logic utilizes modular arithmetic to determine the status of any given date based on a fixed cycle of 4 days.

CycleIndex = ((Date_target − Date_anchor) ÷ 1 Day) mod 4

Where:

Step 1. Calculate the difference in days between the target date and your known first shift (Anchor).
Step 2. Apply the modulo 4 operation.
Step 3. Interpret the result:
If CycleIndex = 0 → Work Day
If CycleIndex ∈ {1, 2, 3} → Rest Day

Reference Data

Cycle Phase	Status	Duration	Typical Activity
Phase 1	On Duty (Work)	24 Hours	Active shift, emergency response, station maintenance.
Phase 2	Post-Shift (Sleep-off)	24 Hours	Physical recovery, sleep adjustment, low activity.
Phase 3	Rest Day 1	24 Hours	Full day off, personal time, family activities.
Phase 4	Rest Day 2	24 Hours	Pre-shift preparation, rest, travel.
Total Cycle	Rotation	96 Hours (4 Days)	Repeats continuously throughout the year.
Annual Load	Work Days	~91 Days/Year	Total working hours approx. 2,184 (excluding leave).

Frequently Asked Questions

This tool uses LocalStorage technology. When you generate your calendar, the 'Anchor Date' is saved securely in your browser's internal memory. You can close the tab or restart your computer, and as long as you don't clear your browser cache, your schedule will reappear automatically next time you visit.

The 1/3 schedule is a continuous 4-day cycle that does not care about calendar dates or leap days. The algorithm simply counts forward 96 hours. February 29th is treated just like any other day in the sequence, ensuring your rotation remains accurate regardless of year length.

No. This specific algorithm is hard-coded for the '1/3' (24 hours on, 72 hours off) rotation common in EMERCOM and Fire Services. Other schedules require different modulo factors (e.g., mod 4 for 2/2, mod 4 for Day/Night/48) but different status logic.

In a 1/3 system, there are 4 distinct 'Platoons' or 'Guards'. Your colleague is likely in a different platoon. To fix this, ask them for their next working date and input that as your Anchor Date to view their specific schedule.

The calendar displays the dates, but in emergency services, public holidays are usually treated as standard working days if your shift falls on them. The tool marks your shift purely based on the mathematical rotation, not legal holiday status.