1. The stomach empties on a curve, and we measure it as a half-time
After a meal, the stomach releases its contents gradually. Researchers summarize that curve with a single figure — the gastric emptying half-time (T½): the minutes it takes for half the meal to leave the stomach, usually measured by scintigraphy (tracking a radiolabeled meal with a gamma camera). It’s the standard, well-validated way to compare how fast different meals clear.
Published half-times for ordinary mixed solid meals cluster in a recognizable band, and — importantly — bigger meals take longer:
| Meal measured | Half-emptying time (T½) | Source |
|---|---|---|
| ~267 kcal mixed solid (rice + egg) | median ~69 min (5–95th pct 45–108), n=189 | 1 scintigraphy, multicenter |
| Standard solid test meal | full meal 94 ± 21 min; smaller portions empty faster | 2 scintigraphy |
| ~320 kcal breakfast (egg, toast, milk) | control group ~121 min | 3 scintigraphy |
| Standard meal, healthy adults | 65.9 ± 14.7 min | 4 scintigraphy |
A typical ~300 kcal mixed solid meal lands roughly in the 70–95 minute range, and larger loads run materially longer. That’s the magnitude our baseline is built around.
The honest bridge: half-emptied is not fully empty, and “the stomach is half-clear” is not the same as “you’ll feel great running.” Translating an emptying curve into a “comfortable to train” moment is an editorial judgment, not a measured threshold. That’s why every result is shown as a window and framed as the earliest you’re likely to feel ready — not a green light to push through symptoms.
2. Fat is the primary, dose-dependent brake
Across the literature, dietary fat is the strongest single lever on emptying speed. Fat is described as “a potent inhibitor of gastric emptying because of its high-caloric density,” and an acute fat load “predictably slows gastric emptying markedly.”5 The slowing is dose-related — more fat, more delay6 — and eating fat before a meal markedly slows that meal’s emptying.7 Mechanistically, fat (digested to fatty acids in the small intestine) reduces stomach contractions and raises pressure at the pyloric valve, throttling the outflow.8 So we weight grams of fat the heaviest.
3. Protein slows it too — but less
Protein is a real but lighter brake: whey protein “load-dependently slows gastric emptying” and stimulates the same gut-hormone feedback, yet gram for gram its effect is smaller than fat’s caloric-density effect.9 We give protein a smaller weight than fat, and total calories set the baseline load.
4. Liquids clear faster than solids
A liquid meal — soup, a protein shake — empties faster than an equivalent-calorie solid plate.10 So choosing “Liquid or shake” shortens the estimate; a 200 kcal shake and a 200 kcal sandwich are not the same wait.
5. Workout intensity raises the wait — this part is editorial
Harder efforts mix worse with a full stomach: blood is diverted from the gut, there’s more mechanical jostling, and reflux/cramp risk climbs — running and HIIT are the most affected. The direction is well-accepted physiology. The size of our intensity adjustment, however, is a design choice with a physiological rationale, not a measured constant. We keep it conservative and label it plainly here.
6. Putting it together
wait ≈ (kcal×0.12 + fat_g×1.4 + protein_g×0.6) × intensity × meal-type- kcal × 0.12 — baseline load, scaled so a ~300 kcal solid meal lands near the published T½ band above.
- fat × 1.4, protein × 0.6 — fat weighted as the dominant brake, protein lighter. These coefficients are our editorial weighting, not measured constants.
- intensity — easy 0.75 · moderate 1.0 · vigorous/run 1.2 · high/HIIT 1.4. Editorial, conservative.
- meal-type — solid 1.0 · liquid/shake 0.6, reflecting faster liquid emptying.
- The result is rounded to the nearest 5 minutes and shown as a −25%…+25% window.
Quick-pick meals use sensible published average macros and are labeled approximate — adjust the sliders for your actual food.
7. Who should not rely on a generic timer
This is an estimate, not medical advice. If you have GERD/reflux, diabetes, gastroparesis, or any GI condition, your gastric emptying may differ substantially from these averages, and exercise timing can interact with your condition and medications — please talk to a clinician rather than a calculator. This tool does not diagnose, treat, or manage any condition.
Sources
Primary gastric-emptying and physiology literature the figures above are drawn from. We cite only sources we drew specific figures or statements from — no invented studies, authors, or years.
- Normal solid gastric emptying values measured by scintigraphy using an Asian-style meal (267 kcal): multicenter study, n=189; median T½ 68.7 min. J Neurogastroenterol Motil 2014. pmc.ncbi.nlm.nih.gov/articles/PMC4102158
- Normal gastric emptying scintigraphy values for limited meal ingestion: full-size solid meal T½ 94 ± 21 min; smaller portions empty faster. Dig Dis Sci 2025. pmc.ncbi.nlm.nih.gov/articles/PMC11972169
- Effect of a vibrating capsule on gastric emptying (320 kcal breakfast): control/sham solid T½ ≈ 121 min. ClinicalTrials.gov NCT02736799. clinicaltrials.gov/study/NCT02736799
- 13C-Spirulina gastric emptying breath test vs. scintigraphy: healthy adults T½ 65.9 ± 14.7 min. ClinicalTrials.gov NCT01248221. clinicaltrials.gov/study/NCT01248221
- Relationships between gastric emptying, postprandial glycemia, and incretin hormones — fat as a potent, high-caloric-density inhibitor of emptying. Diabetes Care 2013;36(5):1396. diabetesjournals.org/care/article/36/5/1396
- Control of gastric emptying of fat by lipolytic products — dose-related slowing by liberated fatty acids. Am J Physiol; PMID 8023935. pubmed.ncbi.nlm.nih.gov/8023935
- Effects of fat on gastric emptying of a carbohydrate meal — fat before a meal markedly slows emptying. J Clin Endocrinol Metab 2006; PMID 16537685. pubmed.ncbi.nlm.nih.gov/16537685
- High-fat diet effects on gut motility and duodenal lipid responses — intestinal lipid slows emptying via reduced antral contractions and raised pyloric tone. Am J Physiol Gastrointest Liver Physiol 2003. journals.physiology.org/doi/full/10.1152/ajpgi.00375.2002
- Acute effects of carbohydrate and fat added to protein on gastric emptying — whey protein load-dependently slows emptying. PMC6213197. pmc.ncbi.nlm.nih.gov/articles/PMC6213197
- Simultaneous measurement of gastric emptying of a soup (liquid) test meal by MRI and scintigraphy — liquids empty faster than equicaloric solids. PMC7151156. pmc.ncbi.nlm.nih.gov/articles/PMC7151156
Figures are population averages from healthy adults and vary by individual, sex, meal composition, and measurement method. Last reviewed: June 8, 2026.