{
  "slug": "add-days-to-date",
  "title": "Date Add / Subtract Calculator",
  "heading": "Add or Subtract Days From a Date",
  "category": "other",
  "url": "https://www.revenuelab.fyi/toolbox/add-days-to-date",
  "summary": "Find the date a number of days, weeks, or months away.",
  "description": "Useful for deadlines, contract notice periods, and return windows. Month arithmetic clamps to the last valid day, so adding one month to January 31 gives February 28 or 29.",
  "formula": "Result = Start date + days + weeks × 7 + months + years.",
  "dateModified": "2026-09-30",
  "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=add-days-to-date",
  "inputs": [
    {
      "id": "start",
      "label": "Start date",
      "kind": "date",
      "hint": null,
      "default": null
    },
    {
      "id": "days",
      "label": "Days to add",
      "kind": "number",
      "hint": null,
      "default": 30,
      "unit": null,
      "min": null,
      "max": null
    },
    {
      "id": "weeks",
      "label": "Weeks to add",
      "kind": "number",
      "hint": null,
      "default": 0,
      "unit": null,
      "min": null,
      "max": null
    },
    {
      "id": "months",
      "label": "Months to add",
      "kind": "number",
      "hint": null,
      "default": 0,
      "unit": null,
      "min": null,
      "max": null
    },
    {
      "id": "years",
      "label": "Years to add",
      "kind": "number",
      "hint": null,
      "default": 0,
      "unit": null,
      "min": null,
      "max": null
    }
  ],
  "outputs": [
    {
      "id": "result",
      "label": "Resulting date",
      "format": "raw",
      "hint": null,
      "primary": true
    },
    {
      "id": "isoDate",
      "label": "ISO format",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "weekday",
      "label": "Day of the week",
      "format": "raw",
      "hint": null,
      "primary": false
    },
    {
      "id": "totalDays",
      "label": "Total days shifted",
      "format": "number",
      "hint": null,
      "primary": false
    },
    {
      "id": "weeksOut",
      "label": "Weeks shifted",
      "format": "decimal",
      "hint": null,
      "primary": false
    },
    {
      "id": "dayOfYear",
      "label": "Day of the year",
      "format": "number",
      "hint": null,
      "primary": false
    }
  ],
  "worked_example": {
    "inputs": [
      "Start date: 2026-09-30",
      "Days to add: 30",
      "Weeks to add: 0",
      "Months to add: 0",
      "Years to add: 0"
    ],
    "outputs": [
      "Resulting date: Friday, October 30, 2026",
      "ISO format: 2026-10-30",
      "Day of the week: Friday",
      "Total days shifted: 30",
      "Weeks shifted: 4.29",
      "Day of the year: 303"
    ]
  },
  "how_to": {
    "title": "How to use this",
    "steps": [
      "Enter start date.",
      "Enter days to add.",
      "Enter weeks to add.",
      "Enter months to add.",
      "Enter years to add.",
      "Read your resulting date on the right — it updates as you type.",
      "Hit Share to keep the scenario or send it to someone."
    ]
  },
  "scenarios": [
    {
      "name": "Conservative",
      "description": "Lower-end numbers — what if things land soft?",
      "values": {
        "start": "2026-09-30",
        "days": 18,
        "weeks": 0,
        "months": 0,
        "years": 0
      }
    },
    {
      "name": "Typical",
      "description": "Defaults — the most common real-world setup.",
      "values": {
        "start": "2026-09-30",
        "days": 30,
        "weeks": 0,
        "months": 0,
        "years": 0
      }
    },
    {
      "name": "Ambitious",
      "description": "Higher-end numbers — what if things really pop?",
      "values": {
        "start": "2026-09-30",
        "days": 48,
        "weeks": 0,
        "months": 0,
        "years": 0
      }
    }
  ],
  "limitations": [
    "Estimates assume standard, average conditions — local rules, pricing, and materials vary.",
    "Results are rounded for readability; add a buffer before ordering, booking, or committing.",
    "Double-check anything with a real cost attached against a local quote."
  ],
  "faq": [
    {
      "q": "How does the add or subtract days from a date work?",
      "a": "Useful for deadlines, contract notice periods, and return windows. Month arithmetic clamps to the last valid day, so adding one month to January 31 gives February 28 or 29. The underlying maths is: Result = Start date + days + weeks × 7 + months + years."
    },
    {
      "q": "What do I need to enter?",
      "a": "5 values: start date, days to add, weeks to add, months to add, and years to add. Each field starts with a sensible default, so you can change one number at a time and watch the result move."
    },
    {
      "q": "What does the resulting date result mean?",
      "a": "It is returned as a plain value and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds."
    },
    {
      "q": "Is this calculator free, and do I need an account?",
      "a": "Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser."
    },
    {
      "q": "How accurate is the result?",
      "a": "It applies the standard formula exactly, so the arithmetic is precise. Estimates assume standard, average conditions — local rules, pricing, and materials vary."
    },
    {
      "q": "Who is this tool for?",
      "a": "It's built for anyone doing everyday planning maths — a quick estimate that would otherwise need four browser tabs and a calculator app."
    }
  ],
  "related": [
    "https://www.revenuelab.fyi/toolbox/days-between-dates",
    "https://www.revenuelab.fyi/toolbox/business-days",
    "https://www.revenuelab.fyi/toolbox/deadline-calculator"
  ],
  "license": "CC-BY-4.0",
  "citation": "RevenueLab — Date Add / Subtract Calculator (https://www.revenuelab.fyi/toolbox/add-days-to-date)"
}