The Losing Trick Count - Facts sheet 6aLosing tricks are counted for the first 3 cards only in each suit.
Therefore you can have at the most 4 x 3 = 12 losers in your hand and 2 x 12 = 24 losers in the combined hands. (the 13th card is excluded from the count)
The actual number of losers in both hands is substracted from 24 (the maximun number of losers possible). This shows the number of tricks you may make:
Counting losers in your hand:
Estimating losers in Partner's hand: