Most cases of stomach flu last one to three days, though some infections can stretch to a week depending on the cause. The worst symptoms, vomiting and watery diarrhea, typically peak within the first 24 to 48 hours and then gradually ease. Here’s what to expect from start to finish.
Timeline by Type of Virus
Norovirus is the most common cause of stomach flu in adults. Symptoms begin 12 to 48 hours after exposure, and the illness typically resolves within one to three days. For most otherwise healthy adults, this is a miserable but short experience: intense vomiting and diarrhea that burns through quickly.
Rotavirus, the leading cause in young children, tends to last longer. Vomiting and watery diarrhea typically persist for three to eight days. In people with healthy immune systems, rotavirus is still self-limiting, but parents should be prepared for a rougher stretch compared to norovirus. Adults can catch rotavirus too, though symptoms are usually milder.
Bacterial Causes Can Take Longer
Not every bout of what feels like stomach flu is caused by a virus. Bacterial infections from contaminated food (think Salmonella, E. coli, or Campylobacter) produce very similar symptoms but can take longer to develop and longer to clear. Most cases of mild, uncomplicated gastroenteritis, whether viral or bacterial, resolve within one to seven days. A key difference: if you ate something contaminated with a bacterial toxin, symptoms can hit within a few hours. If the bacteria itself is multiplying in your gut, it may take a couple of days before you feel sick.
Bacterial gastroenteritis is more likely to produce bloody diarrhea or high fevers. If your symptoms are unusually severe or last beyond a week, a bacterial cause is worth considering.
Day-by-Day Breakdown
Here’s a rough timeline for a typical norovirus infection, the most common scenario:
- Hours 0 to 48 after exposure: No symptoms yet. The virus is replicating in your gut. You may already be contagious during this window.
- Day 1: Symptoms arrive suddenly. Vomiting, watery diarrhea, stomach cramps, and sometimes a low fever. This is usually the worst day. You may not be able to keep anything down.
- Day 2: Vomiting often slows or stops. Diarrhea may continue but becomes less frequent. Fatigue and body aches are common.
- Day 3: Most people feel significantly better. Appetite starts returning. Some lingering diarrhea or nausea is normal.
- Days 4 to 7: Energy gradually returns. Your digestive system may still feel off. Loose stools can linger for a few more days even after the infection clears.
How Long You Stay Contagious
You’re most contagious while you have symptoms and for at least two to three days after they stop. With norovirus specifically, viral particles continue to shed in your stool for days or even weeks after you feel fine, though you’re far less likely to spread the illness once symptoms resolve. This is why thorough handwashing matters even after you’re feeling better. Alcohol-based hand sanitizers are not very effective against norovirus; soap and water is the better choice.
Staying Hydrated During the Worst of It
Dehydration is the main risk of stomach flu, especially in young children and older adults. When you’re losing fluids from both ends, replacing them is more important than eating. Adults with active vomiting or diarrhea should aim for about three liters of fluid per day. For children, roughly one liter per day is a reasonable target. Babies and toddlers need about half a liter daily.
Oral rehydration solutions (available at any pharmacy) work better than water alone because they replace the salts and sugars your body is losing. Small, frequent sips are easier to keep down than large gulps. If you can only manage a tablespoon every few minutes, that still counts.
Sports drinks are a common go-to, but they contain more sugar and less sodium than ideal. They’re better than nothing, but a proper rehydration solution is the more effective option, particularly for children.
When to Eat Again
You don’t need to follow a strict reintroduction schedule. Once your appetite returns, you can go back to eating your normal diet, even if you still have some diarrhea. The old advice about sticking to bland foods like bananas, rice, and toast for days isn’t strongly supported. Eat what appeals to you. The same goes for children: offer their usual foods as soon as they’re interested in eating again.
That said, greasy, spicy, or very rich foods may not sit well on a still-recovering stomach. Most people naturally gravitate toward simpler foods for a day or two, and that instinct is fine to follow.
Warning Signs That Need Medical Attention
Most stomach flu resolves on its own, but certain symptoms signal something more serious. For adults, the red flags include: not being able to keep any liquids down for 24 hours, vomiting or diarrhea lasting more than two days, blood in your vomit or stool, severe stomach pain, signs of dehydration (very dark urine, dizziness, dry mouth, little or no urination), or a fever above 104°F.
Children need closer monitoring because they dehydrate faster. A fever of 102°F or higher, bloody diarrhea, unusual sleepiness or irritability, or signs of significant discomfort all warrant a call to their doctor. For infants, watch for frequent vomiting, no wet diaper in six hours, a dry mouth, crying without tears, or a sunken soft spot on top of the head. Any of these in a baby needs prompt medical evaluation.