All content is for general information only — not medical advice, not a dosing or usage recommendation, and not a claim of efficacy. Many substances are not approved as medicines or are prescription-only; whether possession and use are legal depends on the law of your country of residence and is your own responsibility. myPeptides does not sell or supply any substances — it is an information and organization tool. For health questions, consult a licensed physician or pharmacist.
The forecast is a calculation model, not health advice. Substances marked as prescription only are dispensed on a prescription; investigational substances are not approved as medicines anywhere and are shown here because trials have measured them, not because anyone should take them.
Weight goal forecast
Enter where you are and where you want to be. The tool draws three curves to your target weight: one from a calorie deficit, one from the average weight change published in obesity trials.
Two fields are required, current weight and target weight. Everything else sharpens the estimate.
Advanced options
Enter your current weight and your target weight to see the forecast.
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How the forecast is calculated
In deficit mode the tool steps forward one day at a time for two years. Each day it recalculates your energy expenditure from your current weight with the Mifflin-St Jeor equation and your activity factor, subtracts your intake, and converts the gap into weight at 7700 kilocalories per kilogram. Because expenditure falls with body weight, the curve flattens on its own instead of running in a straight line. Once a scenario reaches your target weight, the line holds there: the model assumes you stop the deficit at the goal.
Metabolic adaptation is applied as an extra reduction in expenditure proportional to the weight already lost. Leibel and colleagues measured a drop in total expenditure of roughly fifteen to twenty percent after a ten percent weight loss, more than the lighter body alone explains, so no adaptation at all is not a scenario this tool offers. The optimistic curve cuts expenditure by half a percent for every percent of body weight lost, the average curve by a full percent, and the pessimistic curve by one and a half percent.
In trial mode the tool takes the published mean weight change of one trial arm and applies that relative curve to your starting weight. Seven of the ten trials report only a baseline and an endpoint, and drawing a straight line between the two would badly understate the early pace: in the trials that do publish intermediate timepoints, sixty to ninety percent of the final effect is already reached at forty to sixty-five percent of the trial duration. The curve is therefore modelled as a saturating exponential that hits the published endpoint exactly and, by default, reaches eighty percent of the effect at half the trial duration, a shape read off the published courses of STEP 1 and SURMOUNT-1. Where intermediate timepoints exist, the shape is fitted to them instead. After the last reported timepoint the curve stays flat: what the trial did not measure, this page does not claim. Every curve is the highest maintenance-dose arm reported as a trial mean, with no dose shown.
The optimistic and pessimistic curves come from the responder shares each trial published, the proportion of participants who lost at least five, ten, fifteen or twenty percent. Assuming a normal distribution, those shares give a standard deviation, and the two outer curves sit roughly at the upper and lower quartile of the trial population. Where a trial published no responder shares, a generic spread is used and labelled as estimated.
Both models ignore everything that actually decides the outcome: illness, sleep, medication, muscle gain, water retention, how measurement days are chosen, and whether the plan is kept at all. Treat the three curves as a range, not as a schedule.
Forecasting from your own progress
In progress mode the tool starts from a measurement instead of an assumption. Your weight at the start, the date it applies to and your weight today give a measured rate. The trial curve or the energy balance then only supplies an expectation, and the ratio between what you actually lost and what was expected becomes a personal factor. The forecast from today is the expected curve scaled by that factor, which is why two people on the same curve get different dates here.
That factor is not applied at full strength straight away. Early weight response predicts the final outcome, but only partly: in the published analyses of liraglutide and semaglutide, people who lose more than the average in the first weeks do tend to end up below the average, yet nowhere near proportionally. The tool therefore pulls the factor back towards one by a weight that grows with the observation window and reaches full strength at twenty-four weeks, and it caps the result between 0.3 and 2.0. Four weeks of double pace is not evidence of a year of double pace.
Evidence for the pull-back towards the average: PMID 27804269 · DOI 10.1210/jendso/bvab048.013
When a ketogenic, low-carb or carnivore style is part of the picture, the first one to two weeks bring a one-off drop of roughly one to three kilograms that is glycogen and the water bound to it, not tissue. That share is subtracted before any rate is calculated, because carrying a one-off effect forward as a weekly rate is the single largest way this kind of forecast goes wrong. If the eating style has not started yet, the same amount appears once in the forecast instead, marked as water in the chart.
Eating styles enter the model in exactly two places: the one-off water shift and, where you say you do not count calories, a change in how much you eat without trying. Where the evidence says the long-term outcome matches an ordinary reduced-calorie diet at the same energy intake, the model adds no lasting bonus. Combining a substance with an eating style adds nothing in the model either, because the trials already ran a lifestyle intervention in both arms.
Diet assumptions in the model
These are modelling assumptions taken from published work, not recommendations. Each row says how strong the underlying evidence is; where there is none, the tool says so instead of hiding it.
| Style | What the model assumes | Intake effect | Water shift | Over | Evidence | Sources |
|---|---|---|---|---|---|---|
| Intermittent fasting | Shifts when you eat, not how much your body spends. Where intake is matched, the weight outcome matches too, so the model only assumes you eat somewhat less without counting, and adds no water shift. | -300 kcal/day | None assumed | — | Meta-analysis of randomised trials | PMID 32673591 · PMID 39813198 · PMID 35443107 |
| Ketogenic or low carb | The fast start is largely water: glycogen leaves and takes its bound water with it, and it comes back when carbohydrates do. At the same energy intake the long-term result does not differ from other reduced-calorie eating. | None assumed | 1–3 kg | 14 days | Meta-analysis of randomised trials | PMID 956398 · PMID 1615908 · PMID 33479499 · PMID 25402637 · PMID 35088407 · PMID 27385608 |
| Carnivore | Modelled like a ketogenic diet because the mechanism is the same. Only one of the sources listed here is about carnivore eating at all, and it is a survey of self-reported outcomes; the others are the ketogenic-diet findings this model carries over. No controlled trial has measured what carnivore eating does to body weight. | None assumed | 1–3 kg | 14 days | No trial data | PMID 34934897Modelled from ketogenic-diet studies: PMID 956398 · PMID 1615908 · PMID 35088407 |
Trial curves behind this tool
Each curve is a published mean from one trial arm. Population, duration and endpoint differ, so the curves are not directly comparable with each other.
| Substance | Trial | Participants | Duration | Endpoint | Status | Source |
|---|---|---|---|---|---|---|
| Semaglutide | STEP 1 | 1306 | 68 weeks | -14.9 % | Prescription only Peer reviewed | Open source |
| Tirzepatide | SURMOUNT-1 | 630 | 72 weeks | -20.9 % | Prescription only Peer reviewed | Open source |
| Retatrutide | phase 2 (NCT04881760) | 338 | 48 weeks | -24.2 % | Investigational Peer reviewed | Open source |
| Cagrilintide | phase 2 (NCT03856047) | 706 | 26 weeks | -10.8 % | Investigational Peer reviewed | Open source |
| Cagrilintide and semaglutide (fixed combination) | REDEFINE 1 | 2108 | 68 weeks | -20.4 % | Investigational Peer reviewed | Open source |
| Eloralintide | phase 2 (NCT06230523) | 263 | 48 weeks | -20 % | Investigational Peer reviewed | Open source |
| Liraglutide | SCALE Obesity and Prediabetes | 2487 | 56 weeks | -8 % | Prescription only Peer reviewed | Open source |
| Orforglipron | ATTAIN-1 | 3127 | 72 weeks | -11.2 % | Prescription only Peer reviewed | Open source |
| Survodutide | SYNCHRONIZE-1 | 242 | 76 weeks | -13 % | Investigational Peer reviewed | Open source |
| Mazdutide | GLORY-1 | 610 | 48 weeks | -14.01 % | Prescription only Peer reviewed | Open source |
Questions about the forecast
How long does it take to lose a given amount of weight?
On a calorie deficit alone, a shortfall of 500 kilocalories a day works out to roughly 0.45 kilograms a week at the start. That rate falls as you get lighter, because a lighter body burns less. Over a year the same deficit therefore yields far less than fifty-two times the first week.
Why does every curve flatten out?
In deficit mode, expenditure falls with body weight until it meets your intake and the loss stops. In trial mode, the curve stops where the trial stopped measuring and stays flat from there, because extrapolating a trend past the data would be invention.
Where do the trial curves come from?
From the published mean weight change of one arm of a registration or main trial, with the source linked for every curve. No dose, no titration schedule and no brand name is shown or implied; the arm is named only as the highest maintenance-dose arm reported as a trial mean.
Will I lose what the trial curve shows?
There is no way to know from this page. A trial mean is the average of hundreds of people whose individual results spread widely around it, which is exactly what the optimistic and pessimistic bands show. Trial averages describe populations, not you.
How accurate is the calorie deficit model?
The energy equations estimate resting expenditure within roughly ten percent for most adults, and the 7700 kilocalories per kilogram constant is a rounded average of fat and lean tissue. Small errors in either compound over months, so read the result as an order of magnitude rather than a date.
Is a faster forecast a better one?
Not on its own. A larger deficit shortens the calculated timeline and also raises the chance of losing lean mass, of an intake below resting expenditure, and of abandoning the plan. If the tool warns that your intake sits below your estimated resting expenditure, that is a question for a doctor.
Why does the forecast not simply carry my current rate forward?
Because almost nobody keeps their first rate. Expenditure falls as you get lighter, the early water is gone once, and adherence drifts. The tool measures your pace, compares it with what the trial curve or the energy balance expected, and then applies that difference only partly, more strongly the longer you have been measuring. Carrying week four forward unchanged would put a date on the calendar that the arithmetic does not support.
I lost three kilograms in the first week on keto. Does that count?
Mostly not, as weight you have taken off your body. Glycogen stores bind roughly three to four grams of water per gram, so emptying them shows up on the scale within days and returns just as quickly when carbohydrates return. The tool subtracts a modelled one to three kilograms before it works out your rate, which is why the forecast looks slower than your first week felt.
Do a substance and a diet add up in this forecast?
No, and the tool says so on screen. The trials behind every curve here already included diet and activity advice in both arms, so their published effect is an effect on top of a lifestyle intervention, not instead of one. Adding a separate diet effect would count the same thing twice.
This article is for informational purposes only and does not replace medical advice. myPeptides gives no dosing recommendations.