{
  "id": "days-until-september-15",
  "version": "6976c6c00c2b",
  "status": "published",
  "name": "Days Until September 15",
  "question": "Days until September 15",
  "summary": "Counts the days from today, or any date you choose, to the next September 15, with its day of the week.",
  "category": "days",
  "subcategory": "countdowns",
  "url": "https://www.acalculator.org/days/days-until-september-15",
  "markdown": "https://www.acalculator.org/days/days-until-september-15.md",
  "kind": "function",
  "method": "Find the first September 15 on or after the start date, then count the days from the start date to it.",
  "assumptions": [
    "September 15 comes every year, so the count is never more than 365 days.",
    "The start date itself is not counted: from the day before September 15, the count is 1; on September 15 itself, it is 0.",
    "Start dates from January 1, 1900 to December 31, 2400 work for the count to September 15, the range the date field accepts.",
    "Today is the date on your own device, so the count to September 15 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 September 15",
      "description": "Whole days from the start date to the next September 15; 0 on the day itself.",
      "format": "integer"
    },
    "date": {
      "label": "Date",
      "description": "The next September 15 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": 350,
      "date": "2027-09-15",
      "weekday": "Wednesday",
      "weeks": "50 weeks"
    },
    "text": "From September 30, 2026, there are 350 days until September 15 on Wednesday, September 15, 2027."
  },
  "examples": [
    {
      "given": {
        "from": "2027-09-15"
      },
      "expect": {
        "date": "2027-09-15",
        "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": "2027-09-15",
        "days": 257
      },
      "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": "2027-09-16"
      },
      "expect": {
        "date": "2028-09-15",
        "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-september-14",
    "days-until-september-16",
    "days-until-september-1",
    "days-until-september-2",
    "days-until-september-3",
    "days-until-september-4",
    "days-until-september-5",
    "days-until-september-6",
    "days-until-september-7",
    "days-until-september-8",
    "days-until-september-9",
    "days-until-september-10",
    "days-until-september-11",
    "days-until-september-12",
    "days-until-september-13",
    "days-until-september-17",
    "days-until-september-18",
    "days-until-september-19",
    "days-until-september-20",
    "days-until-september-21",
    "days-until-september-22",
    "days-until-september-23",
    "days-until-september-24",
    "days-until-september-25",
    "days-until-september-26",
    "days-until-september-27",
    "days-until-september-28",
    "days-until-september-29",
    "days-until-september-30",
    "days-between-dates"
  ],
  "changelog": []
}