Brake pads and rotors get all the attention, but the brake fluid quietly deciding how well those parts work often goes decades without a thought. Fluid is a maintenance item with a real schedule. Here is how often to change it and why the interval exists.
The general interval
Most manufacturers recommend replacing brake fluid every 2 to 3 years regardless of mileage, and some specify it by distance or leave it to a fluid test. Check your owner's manual for the exact figure - it varies by make and by fluid type. The point is that brake fluid ages on a calendar, not just from driving, so a low-mileage car still needs it done.
Why time, not miles
Standard DOT 3 and DOT 4 brake fluid is hygroscopic - it absorbs moisture from the air through seals and hoses over time. Water in the fluid lowers its boiling point, so it can boil under hard braking and give you a soft pedal or fade - see DOT 3 vs DOT 4. Absorbed water also corrodes expensive parts like the ABS unit and calipers from the inside.
Signs it is overdue
Beyond the calendar, watch for a soft or spongy pedal, a faint change in braking on long descents, or dark, dirty-looking fluid in the reservoir - see brake fluid color meaning. Fresh fluid is clear to light amber; coffee-colored fluid is contaminated and overdue. A cheap test strip can confirm moisture content.
The payoff
A fluid flush is one of the cheapest brake services and it protects the costly hydraulic parts while restoring a firm pedal - see the brake fluid flush guide. Pair fresh fluid with quality pads and hardware and your whole brake system stays reliable.