Step by step

You can have this trick as totally  impromptu (without any preparation)   but if you want the trick to have two phases, prepare four black cards into the box in advance.

  1. Ask spectator to shuffle... you prepare your first prediction while he shuffles - "Four more red cards"
  2. Ask spectator to divide the cards in pairs into three piles according to their color - one pile with RED / RED cards, one pile with RED / BLACK cards and one pile with BLACK / BLACK cards
  3. Remove RED / BLACK pile and place them inside card box so they will be now together with cards you prepared in advance inside the box
  4. Next count how many cards are in remaining piles - there will be always four more red cards so your prediction will be correct
  5. Repeat this instantly - take all cards out of the box, ask spectator to shuffle and prepare new prediction - "Same number of red and black cards"
  6. Ask spectator to repeat whole process - your prediction will be again correct! ;)