Extended Fasting Calculator — Free Weight Loss Estimates
Extended fasting means going without food for longer than about 24 hours—and often several days. This free calculator estimates how much of your projected weight loss is burned fat versus temporary glycogen water, so a prolonged fast's headline number doesn't mislead you.
A 10-day duration is pre-selected to model a longer fast, but you can set any number of days. Enter your age, height, weight, and gender for a personalized fat-loss and water-weight breakdown.
Prolonged fasting is not a casual weight-loss shortcut. Multi-day water fasts carry real medical risks and often warrant clinical supervision—use these figures to set expectations, not as a target.
Multi-day modeling
Compounds daily fat loss at your TDEE across the full fast length.
Fat vs. water split
Separates lasting fat loss from the early glycogen water flush.
Vyplňte údaje a kliknete na Vypočítať úbytok hmotnosti pre zobrazení odhadovaného rozdelení.
What to know before you start
What counts as extended fasting?
Most clinicians describe fasts beyond 24 hours as extended or prolonged fasting, distinct from intermittent fasting windows like 16:8. As a fast lengthens, the body shifts from burning liver glycogen toward sustained fat oxidation and ketone production. That is why the first 72 hours show a large water drop on the scale while later days reflect steadier fat loss driven by your total daily energy expenditure.
This calculator uses the Mifflin-St Jeor BMR equation and a sedentary–lightly active TDEE multiplier to project fat loss for each day of the fast, while modeling early glycogen water separately. Because BMR falls with age and lower body mass, two people fasting the same number of days can see very different projected outcomes.
Safety during a prolonged fast
Extended water fasting can affect blood pressure, blood sugar, electrolytes, and heart rhythm. Pregnancy, breastfeeding, being underweight, eating disorders, type 1 diabetes, kidney disease, and many cardiovascular conditions are contraindications for unsupervised prolonged fasting, and several medications may need adjustment.
If you are considering a fast of several days, do it with medical guidance so a clinician can monitor vitals, electrolytes, and safe refeeding. Treat every estimate here as educational—not medical advice or a recommendation to fast longer.
Referenční tabulka úbytku hmotnosti pri vodným pôstu
Príkladové odhady pre muž 35 rokov, 175 cm, 80 kg. Vaše výsledky sa budú líšiť—použite kalkulačku pre personalizovaná čísla.
| Dĺžka pôstu | Vodná hmotnosť | Úbytok tuku | Celkový odhad | BMR / TDEE |
|---|---|---|---|---|
| 3 dní | 1.6 kg | 0.9 kg | 2.5 kg | 1,724 / 2,327 kcal |
| 4 dní | 1.7 kg | 1.2 kg | 3.0 kg | 1,724 / 2,327 kcal |
| 5 dní | 1.9 kg | 1.5 kg | 3.4 kg | 1,724 / 2,327 kcal |
| 7 dní | 2.2 kg | 2.1 kg | 4.3 kg | 1,724 / 2,327 kcal |
Čo sa deje deň po dni
Obecné vzorce behem vodného pôstu—užitečné vedle referenčnúho rozdelení.
| Fáze | Hodiny | Trend vody | Trend tuku | Poznámky |
|---|---|---|---|---|
| Den 1 | 0–24 h | Nízká–strední | Minimální | Glykogen sa začíná vyčerpávat; mírný pokles na váze |
| Den 2 | 24–48 h | Strední–vysoká | Nízká | Úbytok vody sa zrychluje s poklesem glykogénu |
| Den 3 | 48–72 h | Vrchol | Strední | Glykogen z velké části pryč; nejvetší okno vodná hmotnosti |
| Dni 4–5 | 72–120 h | Klesající | Rostoucí podíl | Oxidace tukú tvorí vetší část celkové ztráty |
| Dni 6–7 | 120–168 h | Nízká | Dominantní | Dlhý pôst; často doporučen lékarský dohled |
Odhady používajú BMR Mifflin-St Jeor, TDEE × 1,35, 3 500 kcal/lb tuku a model vody z glykogénu. Ne lekárska rada.
Časté otázky
Odpovede pre túto dĺžku pôstu—pozrite FAQ hlavnej kalkulačky pre kompletné FAQ.
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Pozrite tiež: referenčnú tabuľku, dúveryhodné zdroje, FAQ
Lekárske vyhlásenie · Iba odhady—ne lekárska rada.