Weight Loss Calculator
Compare a calorie-deficit scenario with your estimated energy needs. See the arithmetic timeline to a lower weight, with the assumptions shown beside your result.
Adult educational estimate — this is not a diet prescription or a promise of weight loss. Not for pregnancy, breastfeeding or medically supervised nutrition.
Use the calculatorEstimate Your Weight-Loss Timeline
Adults aged 18–80. Choose your units and compare a scenario.
Your estimate will appear here
Enter your current details and goal. Results describe a scenario, not a diet prescription.
Calorie scenario
Compare estimated maintenance with the selected deficit.
Energy needs
See resting energy (often called BMR) and the activity-adjusted estimate.
Goal arithmetic
A timeline and checkpoints that assume the selected pace stays constant.
Your weight-loss scenario
kcal/day · a starting estimate to discuss, not a prescription
Medical disclaimer: This is an educational estimate, not medical advice or a personalised diet plan. It cannot determine whether weight loss is appropriate for you. Do not use it during pregnancy or breastfeeding, for children, eating disorders or medically supervised nutrition. Discuss calorie intake and weight goals with a qualified clinician or registered dietitian.
Constant-pace checkpoints
Each row is arithmetic, not a forecast. Checkpoints are 30 days apart, not calendar months. Shown for up to 360 days.
Linear scenario only. This is not the dynamic NIH Body Weight Planner model.
| Elapsed days | Calendar date | Scenario weight |
|---|
From energy needs to a weight-loss scenario
Four steps, with the model assumptions visible.
| Step | Arithmetic | Assumption |
|---|---|---|
| 1. Resting energy | 10 × kg + 6.25 × cm − 5 × age + coefficient | Male +5; female −161. Mifflin–St Jeor predicts resting energy, rather than measuring it. |
| 2. Maintenance | Resting estimate × activity factor | Five conventional activity multipliers are simplified choices; they are not part of the original resting-energy equation. |
| 3. Intake scenario | Maintenance − (weekly kg × 7,700 ÷ 7) | 7,700 kcal/kg is a static conversion used for illustration. Real weight change does not follow a fixed rule. |
| 4. Timeline | Days = ceil((current kg − goal kg) ÷ weekly kg × 7) | This is the duration if the selected pace were constant. It is not a predicted completion date. |
Verify the resting formula in the original Mifflin–St Jeor paper; read why the static energy rule is limited in NIDDK’s explanation.
Current-weight estimate
Male coefficient, age 35, 175 cm and 90 kg gives resting energy of 1,823.75 kcal/day. With a ×1.55 activity factor, maintenance is 2,826.81 kcal/day.
A 0.5 kg/week scenario
Static arithmetic gives a 550 kcal/day deficit. Subtracting it from 2,826.81 gives 2,276.81 kcal/day, displayed as 2,277.
The tool does not certify that this intake suits the individual.
A 10 kg difference
From 90 to 80 kg at a constant 0.5 kg/week: 20 weeks or 140 days. From 12 October 2026, the arithmetic date is 1 March 2027.
A calorie estimate is not a guaranteed rate of loss
Keep the model separate from your actual trend.
Why the straight line can mislead
Energy expenditure can change as body weight changes. This tool holds the starting maintenance estimate and chosen pace constant; it does not model those changes.
For a dynamic alternative, use the NIH Body Weight Planner. The result here is a comparison worksheet, not an implementation of that model.
Activity is already counted
The activity multiplier estimates whole-day expenditure. Adding your workout calories to that number again can double-count activity.
Choose a factor that reflects your usual routine. Neither an occupation label nor exercise frequency can establish your exact calorie needs.
How the tool handles restrictive scenarios
No intake scenario is displayed below 1,200 kcal/day with the female coefficient or 1,500 with the male coefficient, above a 25% maintenance deficit, or below the tool’s goal BMI boundary of 18.5. These are conservative product limits, not personalised nutrition standards or proof that other results are suitable. General clinical calorie ranges can be checked in the AHA/ACC/TOS guideline.
CDC describes gradual loss of about 1–2 lb/week as more likely to be maintained than faster loss. That is general guidance, not a rate this calculator can promise for you. Read CDC’s weight-management guidance.
Helpful resources
Related calculators and sources for checking the formula and its limitations.
Useful resources
References are for verification; these organisations do not endorse this calculator. For individual dietary advice, speak to a qualified clinician or registered dietitian.
Questions about your weight-loss estimate
What the numbers mean, and when to seek individual advice.
Is the calorie result a prescription?
No. It is an arithmetic starting point based on an estimated resting energy equation and an activity factor. A clinician or registered dietitian can assess whether weight loss and a calorie target are suitable for you.
Will I reach my goal on the displayed date?
The date shows the arithmetic result of continuing the selected pace without interruption. It is not a forecast. Energy needs, activity, water balance and adherence can change over time.
Why does the calculator block some scenarios?
It does not display intake scenarios below 1,200 kcal/day with the female coefficient or 1,500 with the male coefficient, or deficits above 25% of estimated maintenance. It also blocks goals below its BMI boundary of 18.5. These are tool limits, not a guarantee that other results are appropriate.
Which activity factor should I choose?
Choose the option closest to your usual whole-day activity, not your busiest workout day. These multipliers are simplified assumptions. Do not add exercise calories again to the result because activity is already included.
What do the male and female coefficients mean?
The published Mifflin–St Jeor equation uses different constants for its male and female groups. This selection chooses an equation constant, not a gender assessment. Individual needs may differ; discuss hormone treatment or unusual body composition with a qualified professional.
Is this suitable during pregnancy or breastfeeding?
No. This adult weight-loss estimator is not designed for pregnancy, breastfeeding, children, eating disorders or conditions requiring supervised nutrition.
Does the calculator store my details?
The calculator script processes entries in browser memory. It does not upload entries or save them in browser storage. Other website scripts and services are outside its scope.