Do you need a permit for a day climb of the Grand Teton?

No. Day climbs of the Grand Teton require no permit at all. The permit requirement only kicks in when you camp: any overnight climb, which for most parties means a night at the Lower Saddle at 11,600 feet, requires a backcountry camping permit.

For overnight permits, the advance window opens January 10, and Lower Saddle space in peak season is one of the more contested reservations in the park. Permits are picked up at the Jenny Lake Ranger Station, which is required June through September, so plan that stop before heading up Garnet Canyon. Bear canisters are required for overnight stays.

The day-climb exemption is why strong parties sometimes choose a single-push ascent when they cannot get a camping reservation. It is a legitimate strategy with real costs: roughly 7,000 feet of gain, a start in the small hours, and technical climbing (the easiest line, Owen-Spalding, is 5.4 with a rappel or downclimb on the descent) all in one day.

If your dates are set and the Saddle is booked, camping cancellations do come back through the season as parties change plans, and catching one converts a brutal day into a reasonable two-day climb. Afternoon thunderstorms are the standing hazard either way; the working rule is to be off the summit by noon.