# RuleDate Deadline Calculator

> Business-day and deadline maths with public holidays and a step-by-step rule trace. Chain date operations (add business days, add months with clamping, end of month, roll to next business day) on a start date. RuleDate uses public holidays for 16 countries and their subdivisions (2024–2030) and shows every skipped date with its reason, so the result can be checked rather than trusted.

Part of usefulweb.site (https://usefulweb.site/). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://ruledate.usefulweb.site/ (interactive tool at https://ruledate.usefulweb.site/tool)
- JSON API: POST https://ruledate.usefulweb.site/api/v1/calculate with a JSON object of inputs (schema: https://ruledate.usefulweb.site/api/v1/tool)
- OpenAPI: https://ruledate.usefulweb.site/openapi.json
- MCP (Streamable HTTP): https://ruledate.usefulweb.site/mcp - tool `ruledate`

## Inputs
- startDate (date, required): Start date
- operations (table, required): Operations (applied in order)
- country (select): Holiday calendar
- subdivision (text): Subdivision (optional) - ISO 3166-2 code, e.g. DE-BY (Bavaria), CH-ZH, US-CA. Without it only nationwide holidays count.
- weekendDays (multiselect): Weekend days
- closures (list): Extra closure dates - One YYYY-MM-DD per line (company holidays, bridge days).
- monthEndRule (select): Month arithmetic
- finalRule (select): Final adjustment

## Method
- A business day is a day that is not a selected weekend day, not a public holiday of the chosen country (nationwide, or of the chosen subdivision) and not an extra closure date. Only Nager.Date entries of type "Public" count; bank, school, optional and observance days are ignored.
- Add business days counts business days after the start date (the start date itself is not counted); negative amounts count backwards. Every non-business day passed over is listed with all its reasons.
- Add calendar days / weeks ignore holidays. Add months keeps the day of month; if it does not exist, "clamp" uses the month’s last day and "overflow" rolls into the next month.
- End of month moves to the last calendar day of the month that is `amount` months after the current date. Next / previous business day roll only if the current date is not a business day (following / preceding convention).
- Optional final rule modelled on § 193 BGB: if the result falls on a Saturday, Sunday or a public holiday at the chosen place, it moves to the next day that is none of these (extra closures and custom weekends are ignored for this rule).
- Holiday data covers 2024–2030; dates outside that range are checked for weekends and closures only and trigger a warning.

## Limits
- Not legal advice. Statutory and contractual deadlines have their own rules (start-day exclusion, service dates, court holidays, local holidays); verify critical deadlines with a qualified professional.