The most reliable way is a chest X-ray — pneumonia shows consolidation (a dense shadow in the lung parenchyma) while bronchitis typically shows a normal or near-normal X-ray. Clinically, pneumonia tends to cause higher fever, more significant breathlessness, and oxygen desaturation — but these features overlap. At Pulmovista Clinics, I X-ray every patient with significant respiratory symptoms before prescribing antibiotics, because clinical examination alone cannot reliably make this distinction in Delhi, where pollution and underlying lung disease complicate the picture.