The Losing Trick Count by Tony Philpott with help from Ron Klinger and lots of others

Counting losers is a sound way of estimating the playing strength of a hand, particularly a hand which contains one or two very long suits. High card points are best to assess the value of a balanced hand, counting losers works better for the more distributional hands.

The Losing Trick Count comes into play usually only after you and your partner have established at least an 8-card trump fit. Nevertheless, it often pays with a distributional hand for you to count your losers anyway but don't use it until you know that you and partner have a trump fit. It will give you an idea of the potential of your own cards and if you can gauge how many tricks partner is likely to provide, you can estimate the combined playing strength of the partnership. Should your partner open a 12-14 1NT and you have a very distributional hand you should take it that your partner's 1NT is likely to be an 8-loser hand.

Many systems describe various bids or sequences not just in terms or points, but also in terms of losers or in terms of points and losers. A jump raise by a passed hand (NB-1-3) for example would be described as showing an 8 loser hand. The value is in giving partner a clearer idea of the hand opposite.

Counting your losers in each suit

Void: No losers

Singleton suit: Count one loser, except for ace singleton which has no losers.

Doubleton suit: Count two losers, except for AK (0), Ax (1) or Kx (1.5), but Qx (2, unless the trump suit or partner's 2nd suit).

3-card or longer suit: Count three losers but deduct one for the ace, king or queen.

Examples   
 
AKQ65  =  0 losers     AK  =  0 losers       A  =  0 losers

KQJ93  =  1 loser       KQ4  =  1 loser      K4  =  1 loser

A8765  =  2 losers     KJ4  =  2 losers      94  =  2 losers

J8765  =  3 losers      973  =  3 losers     976542  =  3 losers

In a 3-card or longer suit, count the queen as a winner as long as there is at least one other honour in the suit. If not, count the queen as only half a winner.

AQ765 = 1 loser      QJ764 = 2 losers           Q104 = 2 losers  
KQJ65 = 1 loser      Q8764 = 2.5 losers          Q74 = 2.5 losers

When you find that you and partner have a 9-card fit or better you can deduct 1 loser from your combined total.

Your losers added to your partner's losers is the most convenient way to estimate your combined strength. By deducting this total from 24 suggests the maximum number of tricks that can be made in that suit contract. A combined 14 losers suggests that 10 tricks can be made (24-14) while a combined loser count of 12 suggest that a slam is a possibility (24-12). When partner opens one of a suit you can assume a 7-loser hand and bid accordingly.