{"success":true,"version":"v1","request":{"tool":"get_calculator_schema","calculator_id":"calorie-deficit"},"result":{"entity_type":"calculator","id":"calorie-deficit","calculator_id":"calorie-deficit","canonical_url":"https://tttkmbb.com/health/calorie-deficit","name":"Calorie Deficit & Weight Loss Time Calculator","title":"Calorie Deficit Calculator – Days to Reach a Target Weight","category":"health","category_name":"Health","tool_name":"calculate_calorie_deficit_timeline","featured_mcp_tool":false,"description":"Converts a weight change goal into total energy and the number of days and weeks required at a given daily calorie deficit or surplus, using 7,700 kcal per kilogram of body fat.","use_when":"You know the current and target weight and a planned daily deficit (or surplus) and want a time estimate, or want the deficit needed to hit a date.","do_not_use_when":"You need a medically supervised plan, the target implies more than 1 kg/week loss, or the person is a child; metabolic adaptation makes long projections approximate.","inputs":[{"name":"current_weight_kg","label":"Current weight","type":"number","unit":"kg","required":true,"max":700,"exclusive_min":0,"description":"Current body weight in kilograms.","example":80},{"name":"target_weight_kg","label":"Target weight","type":"number","unit":"kg","required":true,"max":700,"exclusive_min":0,"description":"Goal body weight in kilograms.","example":75},{"name":"daily_deficit_kcal","label":"Daily deficit (or surplus)","type":"number","unit":"kcal/day","required":false,"default":500,"min":50,"max":2000,"description":"Absolute daily calorie deficit (for loss) or surplus (for gain). Sign is inferred from the weight change.","example":500}],"outputs":[{"name":"weight_change_kg","label":"Weight change","type":"number","unit":"kg","decimals":2,"description":"Target minus current weight (negative = loss)."},{"name":"total_energy_kcal","label":"Total energy","type":"number","unit":"kcal","decimals":0,"description":"Energy equivalent of the weight change at 7,700 kcal/kg."},{"name":"days","label":"Days","type":"number","unit":"days","decimals":0,"description":"Days needed at the given daily deficit/surplus."},{"name":"weeks","label":"Weeks","type":"number","unit":"weeks","decimals":1,"description":"Same duration in weeks."},{"name":"weekly_change_kg","label":"Weekly change","type":"number","unit":"kg/week","decimals":2,"description":"Rate of weight change implied by the deficit."}],"input_schema":{"type":"object","properties":{"current_weight_kg":{"description":"Current body weight in kilograms. Unit: kg.","type":"number","maximum":700,"exclusiveMinimum":0,"examples":[80],"x-unit":"kg"},"target_weight_kg":{"description":"Goal body weight in kilograms. Unit: kg.","type":"number","maximum":700,"exclusiveMinimum":0,"examples":[75],"x-unit":"kg"},"daily_deficit_kcal":{"description":"Absolute daily calorie deficit (for loss) or surplus (for gain). Sign is inferred from the weight change. Unit: kcal/day.","type":"number","minimum":50,"maximum":2000,"default":500,"examples":[500],"x-unit":"kcal/day"}},"additionalProperties":false,"required":["current_weight_kg","target_weight_kg"]},"output_schema":{"type":"object","properties":{"weight_change_kg":{"description":"Target minus current weight (negative = loss). Unit: kg.","type":"number","x-unit":"kg"},"total_energy_kcal":{"description":"Energy equivalent of the weight change at 7,700 kcal/kg. Unit: kcal.","type":"number","x-unit":"kcal"},"days":{"description":"Days needed at the given daily deficit/surplus. Unit: days.","type":"number","x-unit":"days"},"weeks":{"description":"Same duration in weeks. Unit: weeks.","type":"number","x-unit":"weeks"},"weekly_change_kg":{"description":"Rate of weight change implied by the deficit. Unit: kg/week.","type":"number","x-unit":"kg/week"}}},"formula":"total_kcal = |target − current| × 7700; days = total_kcal / daily_deficit; weekly_change = daily_deficit × 7 / 7700","method":"The 7,700 kcal/kg (3,500 kcal/lb) rule is a linear approximation; real loss slows as body mass and BMR fall (see Hall et al. 2011 for dynamic models).","sources":[{"name":"Hall KD et al. (2011) Quantification of the effect of energy imbalance on bodyweight, Lancet 378:826-837","url":"https://pubmed.ncbi.nlm.nih.gov/21872751/","type":"peer_reviewed","retrieved_at":"2026-09-23"},{"name":"NIH Body Weight Planner","url":"https://www.niddk.nih.gov/bwp","type":"reference","retrieved_at":"2026-09-23"}],"freshness":{"type":"static","max_age_seconds":null,"note":"Deterministic formula with fixed constants; results never go stale. Inputs supplied by the caller determine the output."},"examples":[{"name":"80 → 75 kg at 500 kcal/day","inputs":{"current_weight_kg":80,"target_weight_kg":75,"daily_deficit_kcal":500},"expected":{"weight_change_kg":-5,"total_energy_kcal":38500,"days":77,"weeks":11,"weekly_change_kg":-0.45},"url":"https://tttkmbb.com/api/v1/calculate/calorie-deficit?current_weight_kg=80&target_weight_kg=75&daily_deficit_kcal=500"}],"faq":[{"q":"Is 500 kcal/day safe?","a":"For most adults a 500 kcal deficit (≈0.45 kg/week) is the commonly recommended upper-moderate rate; do not go below about 1,200 kcal/day (women) or 1,500 kcal/day (men) without supervision."},{"q":"Why is my real loss slower than predicted?","a":"Energy expenditure drops as you lose weight and adherence is rarely perfect. Expect the linear estimate to be optimistic by 20–30% over several months."}],"tags":["calorie deficit","weight loss time","how long to lose weight","3500 calories","7700 kcal"],"related":[{"calculator_id":"tdee","reason":"Find maintenance calories to set the deficit from."}],"links":{"html":"https://tttkmbb.com/health/calorie-deficit","markdown":"https://tttkmbb.com/health/calorie-deficit.md","json":"https://tttkmbb.com/health/calorie-deficit.json","api":"https://tttkmbb.com/api/v1/calculate/calorie-deficit","schema":"https://tttkmbb.com/api/v1/calculators/calorie-deficit","openapi":"https://tttkmbb.com/openapi.json","mcp":"https://tttkmbb.com/mcp"},"version":"v1","updated_at":"2026-09-23"},"timestamp":"2026-09-23T23:31:32Z","next_actions":[{"tool":"run_calculator","calculator_id":"calorie-deficit","reason":"Run Calorie Deficit & Weight Loss Time Calculator with the inputs above."}],"links":{"markdown":"https://tttkmbb.com/health/calorie-deficit.md"}}