A typical common cold runs its course in about a week to ten days. Symptoms usually peak around days 2 to 3 (runny nose, sore throat, sneezing) and then gradually improve. A residual dry cough or mild stuffiness can hang on for two to three weeks even after you feel mostly better, which is normal as the airways recover.
Symptoms that keep getting worse after the first 5 to 7 days, rather than improving, can suggest a secondary infection such as sinusitis or a chest infection. A fever that returns after initially settling is another sign worth attention.
If your symptoms last beyond about 3 weeks, you have a high or persistent fever, you are short of breath, or you feel significantly unwell, contact a doctor or pharmacist. People with asthma, COPD, heart conditions, weakened immune systems, or who are pregnant should seek advice sooner.