Weight Gain Calculator
A 300-calorie daily surplus adds up to 2,100 calories a week, which this calculator converts to about 0.6 lb or 0.27 kg of projected weekly gain. Enter your estimated maintenance calories, planned daily intake, current weight, and goal weight to get a simple weight-gain pace and timeline. The result can help you compare a smaller surplus with a faster plan before you change your food intake. It does not predict exactly how your body weight or body composition will change.
Quick answer
Maintenance calories are the estimated daily intake that would keep your average body weight stable.
What this tells you
- •Maintenance calories are the estimated daily intake that would keep your average body weight stable.
- •Your daily calorie surplus equals planned intake minus maintenance calories, so target intake must be higher than maintenance.
- •The calculator multiplies the daily surplus by seven to find the weekly calorie surplus.
- •It uses 3,500 calories per pound and 7,700 calories per kilogram as fixed planning conversions.
- •The timeline divides the weight you want to gain by the projected weekly rate in your selected unit.
- •The code calculates the timeline from the full unrounded rate, even though the displayed weekly gain is rounded to two decimal places.
- •Real scale weight can rise or fall temporarily because of water, glycogen, sodium, food volume, and bowel contents.
How to Use
- 1Enter your maintenance calories from a recent period of stable weight or from a TDEE estimate. A tracking-based estimate is usually more personal than a formula alone.
- 2Enter the average number of calories you plan to eat each day. It must be greater than your maintenance estimate for the calculator to return a result.
- 3Choose pounds or kilograms, then enter your current weight and a higher goal weight in that same unit.
- 4Calculate to see your daily and weekly surplus, projected gain in both units, and estimated weeks to your goal.
- 5Compare the projected pace with a smaller or larger surplus. Avoid treating the fastest result as automatically better for health or muscle gain.
- 6Track average morning weight under similar conditions for several weeks. Recalculate if your measured trend, intake, activity, or body weight changes meaningfully.
How It Works
Formula
Daily surplus = target calories - maintenance calories
Weekly surplus = daily surplus x 7
Projected weekly gain = weekly surplus / 3,500 kcal per lb or / 7,700 kcal per kg
Weeks to goal = (target weight - current weight) / projected weekly gainThe calculator first subtracts maintenance calories from target calories. For a maintenance estimate of 2,500 kcal and a target of 2,800 kcal, the daily surplus is 300 kcal. Multiplying 300 by seven gives a weekly surplus of 2,100 kcal. The pound estimate is 2,100 / 3,500 = 0.6 lb per week. The kilogram estimate is 2,100 / 7,700 = 0.2727 kg per week, displayed as 0.27 kg. If the selected goal is 10 lb above current weight, the timeline is 10 / 0.6 = 16.7 weeks. The month estimate divides weeks by 4.345, although the current result panel displays weeks. These fixed energy conversions are useful for planning, but human energy use adapts and weight change is not perfectly linear.
Calculation note: values are processed in the order shown above, using the current input units.
Worked Examples
Moderate surplus for a 10 lb goal
Target intake minus maintenance is 2,800 - 2,500 = 300 kcal per day. The weekly surplus is 300 x 7 = 2,100 kcal. Dividing by 3,500 gives 0.6 lb per week. The 10 lb gap divided by 0.6 gives 16.7 weeks, or about 3.8 months under the model's fixed assumptions.
Kilogram goal with a smaller pace
The daily surplus is 2,600 - 2,300 = 300 kcal, and the weekly surplus is 2,100 kcal. Dividing 2,100 by 7,700 gives an unrounded rate of 0.2727 kg per week. The 5 kg gap divided by that full rate gives 18.3 weeks, or about 4.2 months.
Larger pound surplus for a 12 lb goal
The daily surplus is 500 kcal and the weekly surplus is 3,500 kcal. The model converts 3,500 / 3,500 to 1 lb per week. A 12 lb difference at that projected rate takes 12 weeks, or about 2.8 months. This is arithmetic, not a prediction that all 12 lb will be lean tissue.
Slower kilogram plan for a 3 kg goal
The 200 kcal daily difference becomes 1,400 kcal per week. Dividing 1,400 by 7,700 gives 0.1818 kg per week, displayed as 0.18 kg. The calculator divides the 3 kg goal by the full rate and returns 16.5 weeks, which is about 3.8 months.
Small pound surplus for a 5 lb goal
The weekly surplus is 150 x 7 = 1,050 kcal. Dividing by 3,500 gives 0.3 lb per week. A 5 lb goal at that rate takes 5 / 0.3 = 16.7 weeks. A small expected change can be difficult to separate from normal day-to-day scale noise, so weekly averages matter.
Calorie surplus planning examples
Projected weekly gain under the calculator's fixed calorie-to-weight conversions. These figures are planning estimates, not guaranteed outcomes.
| Daily surplus | Weekly surplus | Projected lb/week | Projected kg/week |
|---|---|---|---|
| 150 kcal | 1,050 kcal | 0.30 lb | 0.14 kg |
| 200 kcal | 1,400 kcal | 0.40 lb | 0.18 kg |
| 300 kcal | 2,100 kcal | 0.60 lb | 0.27 kg |
| 400 kcal | 2,800 kcal | 0.80 lb | 0.36 kg |
| 500 kcal | 3,500 kcal | 1.00 lb | 0.45 kg |
The pound and kilogram columns come from separate conversion constants. Rounded rows may not convert exactly from one displayed unit to the other.
Reading a weight trend
A single weigh-in cannot show whether your calorie plan is working. Body weight varies with hydration, carbohydrate intake, sodium, digestion, clothing, and measurement time. Weighing under similar conditions and comparing weekly averages reduces some of that noise.
Give a consistent intake enough time to produce a visible trend before making a large adjustment. If the average remains flat, actual intake may be lower than recorded, maintenance may be higher than estimated, or the observation period may be too short. If weight rises much faster than planned, the surplus may be larger than intended.
Scale change cannot show how much gain came from muscle, fat, water, or stored glycogen. Strength training, adequate protein, sleep, training experience, and individual physiology influence body composition. This calculator models energy and scale weight only.
Common mistakes
- Using a guessed maintenance number without checking it against several weeks of calorie intake and average body-weight data
- Entering target calories that are equal to or below maintenance, which does not create the positive surplus required by this calculator
- Mixing pounds and kilograms between current weight and goal weight instead of using one selected unit for both entries
- Assuming a larger surplus guarantees faster muscle gain when extra energy can also increase fat storage
- Comparing isolated daily weigh-ins instead of averages taken under similar conditions, which makes water changes look like tissue gain or loss
- Treating the estimated week as a deadline even though maintenance needs, appetite, activity, adherence, and scale weight change over time
- Forgetting to update maintenance calories after a meaningful change in weight, training volume, work activity, or daily movement
Limitations
This is a simplified energy-planning model. It assumes maintenance calories remain stable and applies fixed conversions of 3,500 calories per pound and 7,700 calories per kilogram. Actual energy cost per unit of weight change is not fixed because gained weight can include different proportions of fat, muscle, glycogen, water, and digestive contents. The estimate does not model metabolic adaptation, changes in spontaneous movement, training workload, food absorption, menstrual-cycle effects, medications, illness, or fluid retention. Maintenance calorie estimates can also be wrong, especially when intake tracking is incomplete. The result is not designed for children, pregnancy, breastfeeding, recovery from an eating disorder, unexplained weight loss, or nutrition management for a medical condition.
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