Mark your calendars! There are fewer days you can enjoy national parks for free next year.

The National Park Service announced there would only be four fee-free days in 2018.

In 2017, there were 10 free days. And the year before that, as the National Park Service turned 100 years old, there were 16.

The fee-free dates in 2018 include:

  • Jan. 15: Martin Luther King Jr. Day
  • April 21: First day of National Park Week
  • Sept. 22: National Public Lands Day
  • Nov. 11: Veterans Day

The sharp decrease in the number of fee-free days comes as the National Park Service faces a maintenance backlog of more than $11 billion.

The NPS is also considering a fee increase at 17 parks — including the Grand Canyon —during the parks’ busiest five-month periods.

The entrance fee would be $70 per vehicle, up from $30 for a weekly pass.

The fees would also increase to $50 per motorcycle and $30 per person on bike or foot, up from $25 per motorcycle and $15 per individual.

Estimates suggest the fee hike could increase national park revenue by $70 million per year, according to the NPS.

The public has until Dec. 22 to comment on the fee increase decision.