{
  "id": "days-until-october-18",
  "version": "a78b500f5270",
  "status": "published",
  "name": "Days Until October 18",
  "question": "Days until October 18",
  "summary": "Counts the days from today, or any date you choose, to the next October 18, with its day of the week.",
  "category": "days",
  "subcategory": "countdowns",
  "url": "https://www.acalculator.org/days/days-until-october-18",
  "markdown": "https://www.acalculator.org/days/days-until-october-18.md",
  "kind": "function",
  "method": "Find the first October 18 on or after the start date, then count the days from the start date to it.",
  "assumptions": [
    "October 18 comes every year, so the count is never more than 365 days.",
    "The start date itself is not counted: from the day before October 18, the count is 1; on October 18 itself, it is 0.",
    "Start dates from January 1, 1900 to December 31, 2400 work for the count to October 18, the range the date field accepts.",
    "Today is the date on your own device, so the count to October 18 changes at midnight where you are. Dates are whole calendar days, so a daylight-saving change never adds or loses a day."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "from": {
        "title": "Count from",
        "description": "The date to count from. Today, unless you change it.",
        "type": "string",
        "format": "date"
      }
    }
  },
  "outputs": {
    "days": {
      "label": "Days until October 18",
      "description": "Whole days from the start date to the next October 18; 0 on the day itself.",
      "format": "integer"
    },
    "date": {
      "label": "Date",
      "description": "The next October 18 on or after the start date.",
      "format": "date-long"
    },
    "weekday": {
      "label": "Day of the week",
      "description": "The weekday of that date.",
      "format": "text"
    },
    "weeks": {
      "label": "In weeks",
      "description": "The same number of days in weeks and days.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "from": "2026-09-30"
    },
    "outputs": {
      "days": 18,
      "date": "2026-10-18",
      "weekday": "Sunday",
      "weeks": "2 weeks and 4 days"
    },
    "text": "From September 30, 2026, there are 18 days until October 18 on Sunday, October 18, 2026."
  },
  "examples": [
    {
      "given": {
        "from": "2027-10-18"
      },
      "expect": {
        "date": "2027-10-18",
        "days": 0
      },
      "source": "U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years); Python 3 datetime (docs/progress/WP-44/truth.py)"
    },
    {
      "given": {
        "from": "2027-01-01"
      },
      "expect": {
        "date": "2027-10-18",
        "days": 290
      },
      "source": "U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years); Python 3 datetime (docs/progress/WP-44/truth.py)"
    },
    {
      "given": {
        "from": "2027-10-19"
      },
      "expect": {
        "date": "2028-10-18",
        "days": 365
      },
      "source": "U.S. Naval Observatory, Leap Years: the Gregorian leap year rule (https://aa.usno.navy.mil/faq/leap_years); Python 3 datetime (docs/progress/WP-44/truth.py)"
    }
  ],
  "sources": [
    "5 U.S.C. 6103 (federal holidays; weekend rule in 6103(b) and Executive Order 11582). Checked against OPM holiday schedules.",
    "Equinoxes and solstices: Jean Meeus, Astronomical Algorithms (2nd ed., 1998), chapter 27, checked against the US Naval Observatory."
  ],
  "related": [
    "days-until-october-17",
    "days-until-october-19",
    "days-until-october-1",
    "days-until-october-2",
    "days-until-october-3",
    "days-until-october-4",
    "days-until-october-5",
    "days-until-october-6",
    "days-until-october-7",
    "days-until-october-8",
    "days-until-october-9",
    "days-until-october-10",
    "days-until-october-11",
    "days-until-october-12",
    "days-until-october-13",
    "days-until-october-14",
    "days-until-october-15",
    "days-until-october-16",
    "days-until-october-20",
    "days-until-october-21",
    "days-until-october-22",
    "days-until-october-23",
    "days-until-october-24",
    "days-until-october-25",
    "days-until-october-26",
    "days-until-october-27",
    "days-until-october-28",
    "days-until-october-29",
    "days-until-october-30",
    "days-until-october-31",
    "days-between-dates"
  ],
  "changelog": []
}