There is no single gutter cleaning interval that suits every home. A relatively open property may need attention once or twice a year, while a house surrounded by mature gums can fill much faster.
The most useful approach is to inspect gutters after heavy leaf fall and before periods of sustained rain. Overflow marks, plants growing from the gutter, water spilling behind fascia and downpipes that do not discharge normally are all signs that attention is overdue.
Regular cleaning is usually simpler and less expensive than responding after water has reached eaves, walls or foundations. If safe access is uncertain, use a properly equipped professional rather than working from a ladder.