{
  "id": "weight-loss",
  "version": "0fee177a8750",
  "status": "published",
  "name": "Weight Loss Calculator",
  "question": "What is my weight loss timeline?",
  "summary": "Estimates how long it takes to reach a goal weight eating a fixed number of calories a day, with daily energy needs (Mifflin-St Jeor or Harris-Benedict × activity) falling as weight falls.",
  "category": "health",
  "subcategory": "nutrition",
  "url": "https://www.acalculator.org/health/weight-loss-calculator",
  "markdown": "https://www.acalculator.org/health/weight-loss-calculator.md",
  "kind": "function",
  "method": "Days to goal = (7,716.2 ÷ s) × ln(D₀ ÷ D_g), where D₀ and D_g are the daily deficits (TDEE − intake) at the current and goal weights and s is the fall in TDEE per kilogram (activity factor × BMR weight coefficient).",
  "assumptions": [
    "A pound of body weight is 3,500 calories (7,716.2 calories a kilogram).",
    "Daily needs are the BMR (Mifflin-St Jeor or revised Harris-Benedict) × the activity factor, recomputed continuously as weight falls; age, height and activity stay as entered.",
    "The daily intake stays the same until the goal. The goal date rounds the days up to a whole day.",
    "Other changes the body makes during a diet are left out, so real loss is often slower still.",
    "This is an estimate for planning, not medical advice."
  ],
  "inputs": {
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
      "sex": {
        "title": "Sex",
        "description": "Sex at birth, which the body formulas use.",
        "type": "string",
        "enum": [
          "male",
          "female"
        ]
      },
      "age": {
        "title": "Age",
        "description": "Your age in whole years.",
        "type": "integer",
        "minimum": 18,
        "maximum": 100
      },
      "height": {
        "title": "Height",
        "description": "Your height without shoes.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "length",
        "minimum": 0.9,
        "maximum": 3
      },
      "weight": {
        "title": "Weight",
        "description": "Your body weight.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 25,
        "maximum": 700
      },
      "activity": {
        "title": "Activity",
        "description": "How active you are in a usual week, which sets the multiplier on your BMR.",
        "type": "string",
        "enum": [
          "sedentary",
          "light",
          "moderate",
          "very",
          "extra"
        ]
      },
      "goal": {
        "title": "Goal weight",
        "description": "The weight you want to reach.",
        "type": [
          "number",
          "string"
        ],
        "x-quantity": "mass",
        "minimum": 20,
        "maximum": 700
      },
      "intake": {
        "title": "Calories you eat a day",
        "description": "The calories you plan to eat each day until you reach your goal.",
        "type": "number",
        "minimum": 500,
        "maximum": 10000
      },
      "start": {
        "title": "Start date",
        "description": "The day you start. Today, unless you change it.",
        "type": "string",
        "format": "date"
      },
      "formula": {
        "title": "BMR formula",
        "description": "The equation for basal metabolic rate: Mifflin-St Jeor (1990) or the revised Harris-Benedict (1984).",
        "type": "string",
        "enum": [
          "mifflin",
          "harris"
        ]
      }
    }
  },
  "outputs": {
    "date": {
      "label": "You reach your goal on",
      "description": "The date you reach the goal weight: the start date plus the days to the goal, rounded up.",
      "format": "date"
    },
    "weeks": {
      "label": "Weeks to your goal",
      "description": "Time to the goal weight in weeks, with daily needs falling as weight falls.",
      "format": "number"
    },
    "days": {
      "label": "Days to your goal",
      "description": "Time to the goal weight in whole days, rounded up.",
      "format": "integer"
    },
    "tdee": {
      "label": "Calories you burn now (TDEE)",
      "description": "Total daily energy expenditure at your current weight: BMR × activity factor.",
      "format": "number"
    },
    "deficit": {
      "label": "Daily deficit now",
      "description": "TDEE at your current weight minus the calories you eat.",
      "format": "number"
    },
    "tdeeGoal": {
      "label": "Calories you burn at your goal weight",
      "description": "TDEE at the goal weight, which is lower, so the deficit shrinks as you lose.",
      "format": "number"
    },
    "firstWeek": {
      "label": "Loss in the first week",
      "description": "Weight lost in the first 7 days.",
      "format": "quantity",
      "unit": "lb"
    },
    "simpleWeeks": {
      "label": "Weeks by the 3,500-calorie rule",
      "description": "Weeks to the goal if the deficit stayed at its starting size: the simple 3,500-calories-per-pound rule.",
      "format": "number"
    },
    "limit": {
      "label": "Note",
      "description": "A warning when the daily intake is below the lowest intake the weight-loss guideline suggests.",
      "format": "text"
    }
  },
  "defaultAnswer": {
    "inputs": {
      "sex": "female",
      "age": 30,
      "height": 1.651,
      "weight": 68.0388555,
      "activity": "light",
      "goal": 63.502931800000006,
      "intake": 1600,
      "start": "2026-09-29",
      "formula": "mifflin"
    },
    "outputs": {
      "date": "2027-01-26",
      "weeks": 16.98064702081957,
      "days": 119,
      "tdee": 1926.737388125,
      "deficit": 326.73738812500005,
      "tdeeGoal": 1864.3684372500002,
      "firstWeek": 0.29457014990247055,
      "simpleWeeks": 15.302809478562452
    },
    "text": "Eating 1,600 calories a day, you reach your goal weight in about 17 weeks, on January 26, 2027."
  },
  "examples": [
    {
      "given": {
        "sex": "female",
        "age": 30,
        "height": 1.651,
        "weight": 68.0388555,
        "activity": "light",
        "formula": "mifflin",
        "goal": 63.502931800000006,
        "intake": 1500,
        "start": "2026-10-01"
      },
      "expect": {
        "tdee": 1926.737388125,
        "deficit": 426.73738812500005,
        "tdeeGoal": 1864.3684372500002,
        "weeks": 12.66682056908064,
        "days": 89,
        "date": "2026-12-29",
        "firstWeek": 0.3847251675430525,
        "simpleWeeks": 11.716807899043024
      },
      "source": "Mifflin et al. 1990; 3,500 kcal per lb (Wishnofsky 1958); closed-form solution in content.mdx"
    },
    {
      "given": {
        "sex": "male",
        "age": 40,
        "height": 1.8,
        "weight": 100,
        "activity": "moderate",
        "formula": "mifflin",
        "goal": 90,
        "intake": 2000,
        "start": "2027-01-01"
      },
      "expect": {
        "tdee": 2991.5,
        "deficit": 991.5,
        "weeks": 12.089327460715447,
        "date": "2027-03-27",
        "simpleWeeks": 11.117612818198566
      },
      "source": "Mifflin et al. 1990; 3,500 kcal per lb; hand calculation in content.mdx"
    },
    {
      "given": {
        "sex": "female",
        "age": 50,
        "height": 1.65,
        "weight": 80,
        "activity": "sedentary",
        "formula": "harris",
        "goal": 75,
        "intake": 1300,
        "start": "2026-09-27"
      },
      "expect": {
        "tdee": 1778.4276000000002,
        "weeks": 12.244724030206372,
        "days": 86,
        "date": "2026-12-22"
      },
      "source": "Roza and Shizgal 1984 (revised Harris-Benedict); 3,500 kcal per lb; hand calculation in content.mdx"
    }
  ],
  "sources": [
    "Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247. https://doi.org/10.1093/ajcn/51.2.241",
    "Roza AM, Shizgal HM. The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182. https://doi.org/10.1093/ajcn/40.1.168",
    "FAO/WHO/UNU. Human energy requirements (2004), section 5.3.1, Classification of physical activity levels (PAL = TEE ÷ BMR). https://www.fao.org/4/y5686e/y5686e07.htm",
    "Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr. 1958;6(5):542-546. https://doi.org/10.1093/ajcn/6.5.542",
    "Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet. 2011;378(9793):826-837. https://doi.org/10.1016/S0140-6736(11)60812-X",
    "Thomas DM, et al. Can a weight loss of one pound a week be achieved with a 3500-kcal deficit? Commentary on a commonly accepted rule. Int J Obes. 2013;37(12):1611-1613. https://doi.org/10.1038/ijo.2013.51",
    "Jensen MD, Ryan DH, Apovian CM, et al. 2013 AHA/ACC/TOS Guideline for the Management of Overweight and Obesity in Adults. Circulation. 2014;129(25 Suppl 2):S102-S138. https://pmc.ncbi.nlm.nih.gov/articles/PMC5819889/",
    "Centers for Disease Control and Prevention. Steps for Losing Weight. https://www.cdc.gov/healthy-weight-growth/losing-weight/index.html"
  ],
  "related": [
    "calorie-deficit",
    "calorie",
    "tdee",
    "bmi"
  ],
  "changelog": [
    {
      "date": "2026-09-28",
      "note": "Shorter activity labels so they fit the select at 375 px."
    }
  ]
}