initial requirements

Stock > $5.00
For stocks above $5.00 a share, the initial requirement for short stock is typically 50% or $5 a share, whichever is greater. Some stocks may have elevated margin requirements.  
 

Stock <= $5.00
For stocks at or below $5.00 a share, the initial requirement for short stock is 100% or $2.50 a share, whichever is greater.
 

maintenance requirements

Stock > $5.00
For stocks above $5.00 a share, the maintenance requirement for short stock is typically 30% or $5 a share, whichever is greater. Some stocks may have elevated margin requirements.
 

Stock <= $5.00
For stocks at or below $5.00 a share, the maintenance requirement for short stock is 100% or $2.50 a share, whichever is greater.