Calorie Deficit Calculator
Estimate the daily energy deficit needed to reach a lower target weight by a chosen date, then see a practical calorie-intake projection based on Mifflin – St Jeor resting energy needs and your activity level.
Personal details
Metric inputsUsed in the Mifflin – St Jeor resting-energy equation.
Years; enter a whole number from 18 to 100.
Centimetres; accepted range 100 – 250 cm.
Kilograms; enter 30 – 350 kg.
Kilograms; must be lower than current weight.
Choose a future calendar date.
Multiplier applied to estimated resting energy expenditure.
Results
Live estimateEnter a complete valid set of details to calculate a plan.
Equivalent to about 0.30 kg per week under the linear 3,500-kcal-per-pound approximation.
Estimated daily deficit 331 kilocalories; starting intake plan 1,974 kilocalories per day.
Projected weight path
This line follows the calculator's linear target-date projection from current weight to target weight. It is a planning path, not a forecast of day-to-day scale readings.
Start: 74.0 kg
Goal: 68.0 kg
Duration: 20.0 weeks
Scale note: The vertical axis is zoomed to the planned weight range so the change is readable; it does not begin at zero.
Actual body weight commonly fluctuates around any trend because of hydration, food mass, sodium, glycogen, and other factors.
Calorie intake plan
| Week | Date | Projected weight | Estimated TDEE | Planned intake |
|---|
Alternative deficit scenarios
| Daily deficit | Approx. weekly loss | Estimated time to target | Estimated target date |
|---|
How to use this calorie deficit calculator
What this calculator does
This calculator estimates the average daily calorie deficit required to move from your current weight to a lower target weight by a future date. It first estimates resting energy expenditure with the Mifflin – St Jeor equation, then multiplies that value by an activity factor to estimate total daily energy expenditure (TDEE). The deadline determines how much stored-energy change is implied per day. The result is a planning estimate: it does not diagnose health, measure your metabolism directly, or predict the exact rate at which an individual body will lose fat. The original Mifflin – St Jeor research is available through the PubMed record for the resting-energy equation.
When to use it
Use the calculator when you want to compare a weight goal with a deadline, check whether a planned timeline implies a mild or large energy gap, see how estimated maintenance calories relate to a target intake, or compare a target-date plan with fixed 300, 400, and 500 kcal/day deficit scenarios. It is most useful as a starting framework for adults who want to understand the arithmetic behind a calorie-deficit plan.
How to calculate
- The calculator opens with a complete demonstration: female, age 34, height 165 cm, current weight 74 kg, target weight 68 kg, moderate activity, and a target date 140 days from the day the calculator loads. The example XLSX workbook is validated immediately, so Download Excel is available on first open.
- Replace the demonstration values with your own complete set. Changes recalculate instantly; there is no separate Calculate button. Choose the Sex option used by the equation and enter Age as a whole number from 18 to 100.
- Enter Height in centimetres, Current weight in kilograms, and a lower Target weight in kilograms. Enter plain decimal numbers with a period as the decimal separator; scientific notation, unit text, and ambiguous comma decimals are rejected.
- Choose a future Target date and select the Activity level that best describes your usual routine. The activity choice changes estimated TDEE, but it does not change the weight-loss energy gap implied by the goal and deadline.
- Read Calorie deficit to reach goal first, then review Resting energy estimate, Maintenance calories (TDEE), Starting calorie intake plan, Weight to lose, Time available, and Estimated weekly loss. The projection chart and table show the same goal path from different angles.
- Use Download Excel to export the current validated inputs, outputs, projection, and scenario checks as a real .xlsx workbook. Reset clears the demonstration and all user-entered data; after Reset, Download Excel is disabled until a complete valid state is entered again.
Input guide
Sex is required and selects the sex-specific constant used in Mifflin – St Jeor; choose Female or Male. Age is required in whole years from 18 to 100; 34 is the demonstration value, and a higher age lowers the resting-energy estimate when other inputs stay fixed. Height is required in centimetres from 100 to 250; the example is 165 cm, and greater height raises the resting-energy estimate. Current weight is required in kilograms from 30 to 350; the example is 74 kg, and a higher current weight increases estimated resting energy and also changes the amount of weight to lose. Target weight is required in kilograms in the same supported range and must be lower than current weight; the example is 68 kg. Entering the same or a higher value is rejected because this tool is specifically a deficit-to-lower-weight calculator. Target date is required and must be after today; the demonstration uses 140 days from load time. A sooner date increases the required daily deficit, while a later date decreases it. Activity level is required and uses factors from 1.2 for sedentary through 2.3 for a professional athlete; the demonstration uses 1.6. Overstating activity can overstate TDEE and therefore the intake figure.
Output guide
Calorie deficit to reach goal is the average kcal/day gap implied by the weight change and deadline. Resting energy estimate is the Mifflin – St Jeor estimate before activity. Maintenance calories (TDEE) multiplies resting energy by Activity level. Starting calorie intake plan subtracts the required deficit from current TDEE; it is an estimate, not a prescribed intake. Weight to lose is the exact difference between Current weight and Target weight. Time available is the date difference in weeks. Estimated weekly loss converts the target-date deficit back to a weekly weight-rate approximation. In the Calorie intake plan table, Week and Date identify each checkpoint; Projected weight follows a straight-line goal path; Estimated TDEE recalculates energy needs at that projected weight; Planned intake subtracts the same daily deficit. The Projected weight path chart plots those same weight checkpoints. The Alternative deficit scenarios table shows how fixed 300, 400, and 500 kcal/day deficits change the approximate weekly rate and time to the same target.
Worked example
With the demonstration values of female, age 34, 165 cm, 74 kg, 68 kg target, moderate activity factor 1.6, and 140 days available, Mifflin – St Jeor gives 1,440.25 kcal/day of resting energy. Multiplying by 1.6 gives 2,304.40 kcal/day of estimated TDEE. The planned loss is 6.0 kg, equivalent to about 13.23 lb. Using the common planning approximation of 3,500 kcal per pound gives roughly 46,297 kcal of total energy gap; divided by 140 days, that is about 331 kcal/day. Subtracting that gap from the starting TDEE produces a starting intake plan of about 1,974 kcal/day, and the linear target pace is 0.30 kg per week.
Learn more
Weight change is more complex than a fixed energy rule, especially over longer periods. The U.S. National Institute of Diabetes and Digestive and Kidney Diseases provides a dynamic Body Weight Planner and explanation of its scope. For a broader discussion of gradual weight loss and the importance of nutrition, activity, sleep, and stress, see the CDC's steps for losing weight.
How the model works and where it can be wrong
Mifflin – St Jeor: resting energy = 10 × weight(kg) + 6.25 × height(cm) – 5 × age + sex constant, where the constant is +5 for men and – 161 for women. Estimated TDEE = resting energy × activity factor. Required daily deficit = weight change in pounds × 3,500 ÷ days to target. Starting intake plan = TDEE – required daily deficit.
The first two steps estimate energy expenditure from population equations, not from direct metabolic measurement. The activity factor is especially uncertain because two people who describe themselves as “moderately active” may move very differently through the day. The final step uses the traditional 3,500 kcal per pound rule as a transparent planning shortcut. Human weight change does not stay perfectly linear because energy expenditure, appetite, body composition, water balance, and activity can change during weight loss. That is why the calculator also recalculates estimated TDEE along the projected weight path rather than pretending maintenance calories stay fixed.
The weekly projection should therefore be read as a goal line, not a promise. Short-term scale readings can move above or below that line without showing a true change in fat mass. A useful interpretation is to compare multi-week trends rather than expecting every weekly checkpoint to match exactly.
Interpreting a larger or smaller deficit
A shorter deadline increases the calculated deficit because the same target weight change is spread across fewer days. A longer deadline lowers it. Similarly, a larger difference between Current weight and Target weight raises the required gap when the deadline is held constant. Activity level behaves differently: it changes TDEE and the estimated intake that corresponds to the same deficit, but it does not change the deficit required by the weight-and-date arithmetic.
The CDC notes that people who lose weight at a gradual, steady pace are more likely to keep it off, and it emphasizes that healthy weight management also involves eating patterns, physical activity, sleep, and stress. For current U.S. nutrition guidance, the Dietary Guidelines for Americans provides federal guidance on food patterns and nutrient-dense choices. If the calculator produces a very low intake, a very large weekly loss estimate, or a plan that feels difficult to sustain, treat that as a reason to reconsider the assumptions and discuss an appropriate plan with a qualified health professional rather than as a target to force.