St Andrews is busiest in July and August, when golf tourism peaks and the town can feel overwhelmed. The Old Course ballot fills months ahead, parking is difficult, and the main streets are crowded with visitors. That said, the beaches and ruins are large enough to absorb the numbers if you go early in the morning.
May and June are often the best months — the weather can be genuinely warm on the east coast of Scotland (which is drier than the west), the university is still in session so the town has its proper character, and you will not be fighting for restaurant tables. September is also good: the light turns golden, the golf crowds thin, and the sea has held some warmth from summer.
Winter is bleak by any measure — the North Sea wind has nothing to stop it — but the ruins are especially atmospheric in low light, and the town empties almost entirely of visitors. Accommodation prices drop sharply.
The Kate Kennedy Pageant takes place in April: a student procession through the medieval streets re-enacting the founding of the university, with students in historical costume. It is charmingly eccentric and free to watch. The Dunhill Links Championship in October brings the professional golf circus to the Old Course and its Fife coast siblings — worth catching if you are a golf fan, a nuisance if you are not.