Too much direct sun. Filter the harshest midday sun with a sheer curtain for a few weeks, then reintroduce the sunny spot gradually so the leaves can harden off.
What’s causing it
Tap-water salts (a smaller factor here)
How to tell
Ponytail palm tolerates tap-water minerals better than more sensitive foliage plants (calatheas, prayer plants), so this is rarely the main cause. Salts can still build up in a mix that’s never flushed, though.
The fix
If tips keep browning despite correct watering, flush the mix thoroughly with plain water every few months to clear any accumulated salts.
Fertilizer burn (easy to cause on this plant)
How to tell
Brown tips appear with a white crust on the surface. Ponytail palm needs so little feeding that a normal houseplant dose is often already too strong for it.
The fix
Flush thoroughly with plain water, then feed at half the recommended strength and only once or twice a season.
Dry air (low humidity)
How to tell
Just the very tips and edges go brown and papery while the rest of the leaf is fine. This is most common in winter with the heating on, and Ponytail palm prefers 30–60 % humidity.
The fix
Raise humidity with a pebble tray or humidifier nearby. Skip misting directly on the leaves, which can encourage rot on this plant.
Occasional dry spells (a minor factor here)
How to tell
Because Ponytail palm goes long stretches between waterings by design, the very oldest leaf tips can dry and brown even with correct care. This is a much smaller factor than on thirstier plants and rarely the main cause.
The fix
Stick to every 14 to 22 days in summer and don’t compensate for a browning tip by watering more often: that risks the bigger problem, rot.
Prevention
Keep humidity up with a pebble tray or humidifier rather than misting the leaves, water before the mix goes bone dry, and feed lightly.