Weight Loss Calculator

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Age:

Enter whole years, e.g. 34; supported range is 0-120.

Sex:

Choose male or female for formula and floor selection.

Height:

Enter 175 cm, 1.75 m, 69 in, or 5 ft 9 in.

Current weight:

Enter today's weight; kg and lb convert current and goal fields together.

Goal weight:

Enter target weight in the same shared unit as current weight.

Goal schedule:

Select duration for weeks/months, or target date for a deadline.

Start date:

Choose the first day of the projection; defaults to today's plan start.

Timeframe:

Enter the goal duration, e.g. 12 weeks or 3 months.

Goal date:

Choose a date after the start date.

Activity level:

Pick the option that best matches most weeks.

Energy per kg:

Default is 7700 kcal/kg; raise it for a more conservative runway.

kcal/kg

Calorie floor policy:

Choose Safe by sex, None, or Custom for minimum kcal/day handling.

Custom floor:

Enter the lowest kcal/day to allow, such as 1400.

kcal/day

Section	Metric	Value
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Milestone	{{ milestone.label }}	{{ milestone.dateLabel }} {{ milestone.note \|\| '' }}
Recommendation	{{ item.title }}	{{ item.body }}
Pace lane	{{ option.label }}	{{ format(option.calories) }} kcal/day; {{ option.weeklyChangeText }}; finish {{ option.finishDateLabel }}; {{ option.note }}
Plan metric	{{ metric.label }}	{{ metric.value }}

Stage	Date	Weight ({{ weightUnit }})	{{ changeToDateHeader }}	BMI	TDEE	Cal target	Copy
{{ row.label }}	{{ row.dateLabel }}	{{ formatDec(row.weight) }}	{{ formatSigned(row.change) }}	{{ formatDec(row.bmi) }}	{{ format(row.tdee) }}	{{ format(row.cal) }}

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Weight change planning is a moving energy-budget problem, not a single magic calorie number. Body size, age, sex, height, activity, goal weight, and time window all affect the estimate. A 500 kcal/day deficit can be a useful benchmark, but the same deficit has different meaning for a tall active adult, a shorter sedentary adult, and someone already close to a target weight.

The most useful vocabulary separates energy needs from weight status. Basal metabolic rate, or BMR, estimates resting energy use. Total daily energy expenditure, or TDEE, adds an activity multiplier to estimate a normal day's energy use. A deficit means planned intake is below TDEE, while a surplus means planned intake is above it. Body mass index, or BMI, compares weight with height and gives an adult screening category; it does not diagnose health, body composition, or fitness.

Time is the other half of the plan. Losing 8 kg over 24 weeks and losing the same amount over 6 weeks are not just faster and slower versions of the same goal; they imply different calorie targets, different warning levels, and different odds that a minimum calorie floor will block the requested date. Goal maintenance also matters because the calorie target that creates a loss may be too low once the goal is reached.

Scale weight carries noise from water, sodium, carbohydrate intake, training soreness, medication, sleep, menstrual-cycle changes, and digestion. A useful calorie runway should be compared with a multi-week weight trend and real food records, not judged by one weigh-in. Plans for children, teens, pregnancy, lactation, eating-disorder recovery, medication changes, serious illness, or clinically supervised diets need professional guidance rather than a generic adult estimate.

Health note: Calorie and BMI estimates are planning aids. Treat very low intake targets, underweight BMI flags, rapid pace warnings, or symptoms during weight change as reasons to get qualified medical or nutrition advice.

How to Use This Tool:

Use the calculator when you need a daily calorie target tied to a body profile, activity level, goal weight, and date or duration. Start with the most stable facts, then use the warning badges and runway tabs to decide whether the goal needs more time or a different floor.

Enter Age, Sex, Height, Current weight, and Goal weight. Height can be entered as centimeters, meters, inches, or feet plus inches; changing the weight unit converts both current and goal weights together.
Choose the Goal schedule. Duration mode solves from weeks or average calendar months, while date mode uses Start date and Goal date.
If the date is invalid or not after the start date, the calculator shows a validation error instead of a runway.
Select the Activity level that describes most current weeks. Use the routine you can already sustain, because this choice multiplies BMR into the starting TDEE estimate.
Open Advanced only when the defaults do not match the plan. The default energy setting is 7,700 kcal/kg, and Safe by sex applies 1,500 kcal/day for male entries and 1,200 kcal/day for female entries on loss plans.
None removes the calorie floor, and Custom lets you enter a different minimum kcal/day. Those settings change warnings and the projected finish.
Read the summary badges before using the calorie number. They call out maintenance, surplus, selected-window, floor-limited, later-finish, BMI, pace, goal-date, and maintenance cues.
Use Plan Brief for the headline numbers, then compare Goal Runway, Calorie Curve, Pace Lane Map, and Weekly Runway when you need dates, charts, rows, or exportable evidence.
Recheck the inputs if warnings mention under-20 assumptions, BMI below 18.5, a pace faster than the usual 1 to 2 lb/week range, a floor-limited target, or a projected finish that misses the requested date.

Interpreting Results:

The applied calorie target is the number to read first because it includes any calorie-floor adjustment. The unclamped target shows what the schedule would have required before the floor. If those two values differ, the requested date is more aggressive than the selected minimum intake allows.

How to read major weight loss calculator outputs
Output	What to trust	What not to overread
Applied calorie target	The estimated daily intake after the selected floor policy is applied.	It is not a medical prescription or proof that the same intake will work every week.
Opening and goal-line pace	The estimated weekly change near the start and near the end of the projection.	The first-week pace should not be assumed to stay constant through the whole plan.
Goal maintenance estimate	The estimated calories to maintain the goal weight at the same activity setting.	It does not account for future training changes, adaptive appetite, or measured metabolism.
BMI context	Current BMI, goal BMI, and the adult healthy-weight band for the entered height.	BMI is a screening category and can mislead for teens, pregnancy, athletes, or unusual body composition.
Pace Lane Map	Alternative calorie and pace scenarios around the requested goal.	The fastest lane is not automatically the best lane; floor and pace warnings still matter.

A confident plan has internally consistent inputs, no unresolved validation errors, a calorie target above any floor that applies to the person, and a pace that can be checked against real trend data. A warning does not always mean the math failed, but it does mean the goal should be adjusted, reviewed, or treated as a scenario rather than a recommendation.

Technical Details:

Weight-change math starts with an estimated maintenance intake, then applies an intake gap over time. The estimate used here is deterministic: weight and height are normalized to metric units, BMR is estimated from the Mifflin-St Jeor equation, activity multiplies BMR into TDEE, and a day-by-day simulation updates the projected weight.

The adaptive part matters because TDEE is recalculated at each simulated weight. During a loss plan, a smaller body usually has a lower estimated maintenance need, so a fixed calorie target creates a smaller deficit near the goal than at the start. During a gain plan, estimated maintenance rises with projected weight, so the same surplus can narrow near the goal.

Formula Core:

Adult BMI uses body mass in kilograms and height in meters:

BMI = \frac{weight kg}{{height m}^{2}}

The resting estimate uses Mifflin-St Jeor:

BMR = 10 \times weight kg + 6.25 \times height cm - 5 \times age years + sex offset

The sex offset is +5 for male entries and -161 for female entries. TDEE is then:

TDEE = BMR \times activity factor

For each simulated day, the projected weight change comes from the energy gap divided by the selected energy density:

daily change kg = \frac{TDEE - daily calories}{kcal per kg}

A positive daily change in that equation reduces projected weight. A negative value raises projected weight. The default energy-density setting is 7,700 kcal/kg, and the calculator will not use less than 1,000 kcal/kg if the advanced value is lowered too far.

Activity factors used for total daily energy expenditure
Activity level	Factor	Typical fit
Sedentary	1.200	Little or no exercise in a normal week.
Lightly active	1.375	Exercise about 1 to 3 days per week.
Moderately active	1.550	Exercise about 3 to 5 days per week.
Very active	1.725	Exercise 6 to 7 days per week.
Extra active	1.900	Physical job, high-volume training, or two-a-day routines.

Floors, Search, and Boundaries:

The target calories are solved by searching for the intake that lands closest to the goal weight over the selected number of days. For loss plans, the selected calorie floor can raise the solved target. For gain plans, no loss-floor clamp is applied because the goal requires a surplus rather than a cut.

Weight loss calculator boundary conditions and warnings
Boundary	Rule used	Meaning
Adult BMI healthy band	18.5 to 24.9	Used for adult screening context and healthy-weight range by height.
Age warning	Age under 20	Adult BMI and calorie assumptions should be treated as rough screening.
Fast pace warning	Opening loss pace above about 2 lb/week	The plan is faster than common gradual-loss guidance.
Short-window warning	Less than 28 days with more than 0.5 unit of planned change	Weekly pace can look sharper than real trend data supports.
Goal search limit	Calories searched up to 12,000 kcal/day and finish search up to 3,650 days	Extreme or unreachable plans may show a plateau or delayed finish instead of a precise date.

For example, a 35-year-old female entry at 165 cm, 78 kg, moderately active, targeting 70 kg over 24 weeks solves to about 1,855 kcal/day. The starting BMR is about 1,475 kcal/day, starting TDEE is about 2,287 kcal/day, and goal maintenance is about 2,163 kcal/day. The opening pace is about 0.4 kg/week and tapers near the goal because the projected TDEE falls with weight.

Accuracy and Privacy Notes:

Weight change is influenced by physiology and behavior that a form cannot measure directly. Treat the output as an estimate to compare with observed trends.

BMR and TDEE come from population equations, not indirect calorimetry or wearable-verified expenditure.
Activity multipliers are broad. Choosing one level too high or too low can move the calorie target more than small formula differences.
Adult BMI categories are not appropriate as the main interpretation method for children, teens, pregnancy, or many athletic body types.
The calculation runs in the browser after the page loads. Exported CSV, DOCX, chart images, copied rows, URLs, and JSON can contain body measurements, dates, calorie targets, and warnings, so handle them like private health notes.

Worked Examples:

These examples use the same formulas and warning rules as the calculator, so the key lesson is how the same goal changes when the time window or direction changes.

Moderate loss window

A 35-year-old female entry at 165 cm and 78 kg targets 70 kg over 24 weeks with Moderately active selected. The applied target is about 1,855 kcal/day, with no floor clamp. The Plan Brief shows current TDEE near 2,287 kcal/day, goal maintenance near 2,163 kcal/day, and a taper from about 0.4 kg/week at the start toward about 0.3 kg/week near the goal.

Deadline that hits the floor

The same 78 kg to 70 kg target over 6 weeks would solve to roughly 759 kcal/day before safety handling. With Safe by sex active, the applied target rises to 1,200 kcal/day, the plan is marked floor-limited, and the projection finishes near 72.3 kg at the requested date. The warning means the date, goal weight, or calorie floor needs review.

Small surplus goal

A 29-year-old male entry at 178 cm and 70 kg targets 74 kg over 16 weeks with Lightly active selected. The calculator models a surplus of about 303 kcal/day over starting TDEE and returns about 2,603 kcal/day. Because this is a gain plan, loss calorie floors do not clamp the target; the Pace Lane Map switches to gain-style lanes instead.

FAQ:

Why does the projected pace slow during a loss plan?

Estimated TDEE usually falls as projected weight falls. If daily calories stay fixed, the deficit is larger near the start and smaller near the goal.

Why are raw and applied calories different?

Raw calories are the target that best fits the requested schedule. Applied calories are shown after the selected calorie floor is enforced, which can make the projected finish later than requested.

Can I use this for a teenager?

Use it only as a rough adult-equation scenario. The calculator flags age under 20 because children and teens need age- and sex-specific growth-chart interpretation.

Why does the result warn about BMI below 18.5?

A current or goal BMI below 18.5 falls outside the adult healthy-weight screening band used by the calculator, so further loss may be inappropriate without clinical guidance.

Why might my real weight differ from the weekly runway?

Food logging error, changes in activity, water shifts, menstrual-cycle changes, medication, sleep, stress, and metabolic adaptation can all move observed weight away from the projection.

Glossary:

BMR: Basal metabolic rate, an estimate of resting energy use before activity is added.
TDEE: Total daily energy expenditure, estimated as BMR multiplied by an activity factor.
Calorie floor: A minimum daily calorie target that can raise very low loss-plan targets.
Energy density: The kcal/kg assumption used to translate an energy gap into projected body-weight change.
Goal maintenance: The estimated daily calories needed to maintain the goal weight at the selected activity level.
Pace lane: An alternate calorie target that compares the requested plan with gentler, steadier, brisker, or surplus-style scenarios.

References:

Steps for Losing Weight, CDC, January 17, 2025.
Adult BMI Categories, CDC, December 11, 2023.
Eating & Physical Activity to Lose or Maintain Weight, NIDDK.
Body Weight Planner, NIDDK.
A new predictive equation for resting energy expenditure in healthy individuals, The American Journal of Clinical Nutrition, 1990.

Weight Loss Calculator

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Current result

How to Use This Tool:

Interpreting Results:

Technical Details:

Formula Core:

Floors, Search, and Boundaries:

Accuracy and Privacy Notes:

Worked Examples:

Moderate loss window

Deadline that hits the floor

Small surplus goal

FAQ:

Glossary:

References: