Note: There are 3 articles in this series. The start/cover page is here.

Penalty for being defeated (undoubled)

If you are going to go down, it is obviously better if you aren't doubled.

It is less penal if you aren't vulnerable.

Not vulnerable (and not doubled), it costs only 50 per each trick you are set. In an auction where your opponents were going to make their contract, it is usually okay if you play it and can go down only 2 undoubled for -100.  This is better than letting your opponents make just about any contract.  Anything higher than 1NT (90) or 2 or 2 (90) would have paid more than 100 for them.

So, if your opponents were in 2 (110) and going to make it, you are better off paying out 50 (down 1 not vulnerable) or 100 (down 2 not vulnerable).

Even if you are vulnerable, the penalty is -100 for each trick you fail by.  Down 1 (undoubled) for -100 is better than letting them make a contract of 2 or higher.

Of course, there is no sure way to know who is making what, but knowing what the penalties and scores are is useful in your decision making.

Here is the table for going down (undoubled):

For doubled penalties, see this.