The reservation confirmation form that came in the mail states that group size can be increased by calling their office as long as there are spaces available. I called the office this morning to request an additional spot but was told to call again on April 20th. Have people been successful with increasing their group size this way? We need to increase from 4 to 5 for day hike on July 22..
AKJ, welcome to the forum!
July is a high-demand month, so everything is completely booked.
Inyo has just posted the Calendar of Dates still available after the lottery processing has completed-- ...for Day Hikes: Day Use Mt Whitney Zone ...for overnight backpack trips: Overnight Mt Whitney trail
However, I am 99% sure you can add that 5th slot, if you still need all 5 come hike time (MANY groups find that some people drop out at the last minute.) If you want to add, just call the Wilderness Permit office starting a week before your hike. A few good people call in about then and release some or all of their reservations. If you call when one is available, it will be yours. If that doesn't work, when you go to pick up your permits, they will probably have some last-minute cancellations available at that time.
