Symptom guide · Respiratory illness
Flu vs. cold — how to tell the difference
Both start in your nose and throat. Only one is worth an antiviral prescription — and only in the first 48 hours. Here's the side-by-side.
Comparison chart
| Symptom | Influenza (flu) | Common cold |
|---|---|---|
| Onset | Abrupt — fine in the morning, floored by evening | Gradual over 1–3 days |
| Fever | Common, 100–104°F, lasts 3–4 days | Rare, usually low-grade if present |
| Body aches | Common and often severe | Mild if any |
| Chills | Common | Uncommon |
| Fatigue | Marked, can last 2+ weeks | Mild |
| Headache | Common | Uncommon |
| Runny / stuffy nose | Sometimes | Hallmark symptom |
| Sneezing | Sometimes | Common |
| Sore throat | Sometimes | Common |
| Cough | Common, dry and can be severe | Mild to moderate, hacking |
| Typical duration | 5–7 days of illness, cough and fatigue linger | 7–10 days, cough may linger 2–3 weeks |
| Prescription treatment | Oseltamivir (Tamiflu) or baloxavir (Xofluza) within 48 hours | Supportive care; prescriptions only for complications |
When to get seen
- Within 48 hours of sudden fever and body aches — antivirals are time-sensitive.
- Fever above 103°F, or any fever lasting more than 3 days.
- Improving, then suddenly worse — a classic bacterial-complication pattern.
- Shortness of breath, chest pain, confusion, or dehydration — in-person or emergency care.
- Pregnancy, age 65+, asthma or COPD, diabetes, heart disease, or immunosuppression.
Not sure which one you have? Flu treatment online or cold and URI care — same clinician either way.
Frequently asked questions
How can I tell the flu from a cold?
Speed and fever are the biggest tells. Flu arrives abruptly with fever, body aches, chills, headache, and heavy fatigue. A cold builds slowly over a couple of days, stays mostly in the nose and throat, and rarely causes a real fever.
Can a cold turn into the flu?
No — they're different viruses. A cold can, however, be followed by a bacterial sinus infection, ear infection, or bronchitis, which is why symptoms that worsen after initial improvement deserve a look.
Is it flu or COVID?
They overlap almost completely; loss of taste or smell leans COVID but is far from reliable. If treatment eligibility is on the line — antivirals for either — a combined flu/COVID test is the only way to know.
What about RSV?
RSV in adults looks like a bad cold that moves into the chest — wheezing, shortness of breath, and a productive cough. It matters most for infants, older adults, and people with lung disease.
How long am I contagious?
Flu: about a day before symptoms until 5–7 days after. Cold: roughly the first 2–3 days, when symptoms peak. For flu, stay home until 24 hours fever-free without fever reducers.
When should I see a clinician?
Fever above 103°F, symptoms lasting more than 10 days, worsening after improving, shortness of breath, chest pain, confusion, or dehydration. Also worth a visit if you're within 48 hours of flu onset and want antivirals, or you're high-risk.
Feeling worse by the hour?
Book a same-day Ondoc visit — a licensed clinician sorts flu from cold, orders testing when it matters, and prescribes when it helps.