Is the interval calendar based or a fixed elapsed time?
Keep year and month components as calendar units and evaluate them at a stated anchor. Use approximate seconds only for a rough sense check, never to settle a month-end deadline.
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Workflow Playbook
Turn a dated reporting anchor and a stated duration into an auditable calendar endpoint, ISO week label and fiscal-quarter assignment.
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A reporting analyst needs more than a date string to define a defensible period. Record the source value, the authoritative timezone if it denotes an instant, and whether the reporting convention treats the end as included or excluded. Use iso-8601-converter to normalize the starting date or datetime, but keep the original input beside it. If the policy speaks only in dates, do not silently convert those dates into UTC instants. If several teams disagree about the timezone, settle that policy before calculating anything; this workflow does not replace the broader normalization and deadline checks in date-time-scheduling.
Use iso-8601-duration-builder to turn an agreed phrase such as one calendar month into a duration string. Its approximate seconds are a sense check, not a contract for when that month ends. Then use iso-8601-duration-parser-arithmetic-workbench with the same anchor to calculate the endpoint. A month added at the end of January can clamp to the end of February; multiplying by thirty days would answer a different question. If the duration contains mixed weeks or a leading sign, check whether the downstream consumer accepts ISO 8601-2 extensions or requires strict ISO 8601-1 notation. Keep the exact expression in the handoff so another analyst can reproduce the result.
Run iso-week-number-and-fiscal-quarter-anchor on both the start and calculated endpoint. Select the organization's standard, 4-4-5, 4-5-4 or 13-week convention and fiscal-year start month before labeling either date. At New Year, ISO week-year can differ from calendar year; note the full week label rather than just a week number. Finally write a short record containing source, ISO anchor, duration, endpoint, timezone or date-only rule, inclusive/exclusive end and fiscal convention. Recheck an adjacent period for overlap or gaps. For recurring meeting rules or ICS export, switch to calendar-recurrence-and-ics-scheduling; this page describes one reporting window, not a recurrence engine.
Workflow playbook
Convert the supplied date or datetime to a stable ISO representation; preserve the source timezone or declare that the report uses date-only values.
Convert a verbal period to an ISO duration and inspect its components; separate strict ISO 8601-1 notation from optional extensions.
Parse the exact duration and apply calendar-aware arithmetic to the anchor. Check clamping at month ends and compare alternatives only at the same anchor.
Inspect the start and endpoint under the selected fiscal calendar, then record the ISO week-year and quarter alongside the interval convention.
Keep year and month components as calendar units and evaluate them at a stated anchor. Use approximate seconds only for a rough sense check, never to settle a month-end deadline.
Prefer a duration without mixed weeks or a leading sign for strict interchange; inspect any ISO 8601-2 extension before sending it to another system.
Choose standard, 4-4-5, 4-5-4 or equal 13-week quarters from the reporting policy before labeling the start and end dates.