Rotating shift schedule planner

Invalid ranges, impossible calendar days, and out-of-range cycle fields fail with invalid_input and are never billed.

What a rotating on/off cycle means for one worker

Rotating shift patterns such as four-on four-off, two-on two-off, or seven-on seven-off are common in continuous operations where coverage must roll evenly across calendar days without fixing the same weekdays every week. The model here is deliberately simple and transparent: each cycle is an on block of consecutive work days followed by an off block of consecutive rest days; the pair repeats from the start of the requested window. Two-on two-off uses two and two. A five-on two-off pattern uses five and two and produces a work ratio near five sevenths, which is useful when you want more work density than a pure half-time rotation. What it does provide is a reproducible single-worker expansion you can export into spreadsheets, time-clock imports, or payroll previews without reimplementing modular arithmetic in every client. Day zero of the cycle is the first day of an on block when cycle_offset is zero. For any day index i counted from start_date (zero-based), day_in_cycle equals the remainder of i plus cycle_offset divided by cycle_length, where cycle_length is on_days plus off_days. If that remainder is strictly less than on_days the day is on; otherwise it is off. Classic four-on four-off therefore uses on_days four and off_days four, a cycle of eight days, and a long-run work ratio of one half. Setting off_days to zero forces every day on inside the window, which is occasionally useful as a baseline always-available roster. This tool does not assign multiple named crews, does not skip public holidays, does not encode night versus day tour labels beyond the binary on/off status, and does not rebalance hours against labor law maxima—those layers belong in your HR system.

Input contract, response shape, and validation rules

The formula field restates the modular rule in plain text for audit trails. POST a JSON body with four required fields and two optional ones. start_date and end_date must be real Gregorian calendar strings in strict YYYY-MM-DD form; the range is inclusive on both ends and end_date must not precede start_date. The inclusive span may be at most three hundred sixty-six days so response size stays bounded for browser and API clients. on_days is a positive integer from one to ninety; off_days is an integer from zero to ninety. cycle_offset defaults to zero and must lie between zero and cycle_length minus one when supplied, so a mid-hire phase cannot point past the end of the cycle. worker_name is an optional label of at most one hundred twenty characters echoed on success when present. Aliases are accepted for ergonomics: from or begin for start_date, to or until for end_date, work_days for on_days, rest_days for off_days, offset or phase for cycle_offset, and name or employee for worker_name. On success the body returns the normalized dates and cycle parameters, pattern as a short string such as four-on slash four-off, total_days, days_on, days_off, work_ratio rounded half-up to six decimals, a roster array of objects each with date, day_in_cycle, and status on or off, plus parallel on_dates and off_dates string arrays for quick filtering. Impossible dates such as the thirty-first of April, a negative span, a span over the maximum, a zero or non-integer on_days, or a cycle_offset equal to or larger than cycle_length fail with invalid_input naming the field; those failures do not consume prepaid balance. Pricing for successful calls is a flat $0.002 with unit item.

Where rotating roster expansion earns its keep

Site supervisors planning a four-on four-off month need a quick list of which calendar dates a technician works before publishing the notice board. Content and SEO landings that rank for rotating shift schedule planner or four-on four-off roster benefit from a live free calculator whose outputs match the paid automation path byte for byte on the shared lib. Prefer this capability when the question is pure cycle expansion for one person; multi-crew fairness, union rules, skill mixes, and leave calendars need a fuller workforce management product. Failed validation is free, so exploratory clients can probe invalid offsets and bad dates safely. HR onboarding flows can pass a hire date as start_date with a non-zero cycle_offset so the new hire joins the existing rotation mid-cycle instead of restarting at day zero. Payroll preprocessors count days_on inside a pay period to cross-check expected ordinary hours before overtime rules apply. Staffing simulators compare work_ratio across candidate patterns—two-on two-off versus four-on four-off versus five-on two-off—without writing custom scripts each time. Integration teams embed the API in internal tools so schedulers never retype modular tables by hand. Keep requests inside the three hundred sixty-six day cap; for multi-year workforce planning, call the endpoint once per year window and stitch results client-side.