Vulnerable or Not-Vulnerable

Being vulnerable increases bonuses when you make a contract and conversely increases the penalties for going light in your contract.  Vulnerability also affects strategies for a partnership bidding and play. Partnerships tend to be more cautious when they are Vulnerable and take more risks when they are not-vulnerable

Vulnerability:

If Your Contract Goes Light and you Don't Score Enough Tricks

If you fail to make your contract by one or more tricks this is known as “going light”—your opponents score points for each undertrick.

Not Vulnerable Penalty

When you are not vulnerable (“not vul”), and you go lightyour opponents score 50 points per undertrick.

Vulnerable Penalty

When you are vulnerable (“vul”) and go light, the penalty doubles to 100 points per undertrick.

Partnerships should be careful about overbidding when vulnerable and they can take more risks when they are not-vulnerable.

Non-Vulnerable (not-vul) Under tricks penalties:

Down 1 = -50 points
Down 2 = -100 points
Down 3 = -150 points
Down 4 = -200 points

Vulnerable (vul) Under tricks penalty

Down 1 = -100 points
Down 2 = -200 points
Down 3 = -300 points
Down 4 = -400 points

Making Your Contract

If you are not vulnerable (“not vul”) and successfully bid and make a game contract, you score a 300 point bonus in addition to the points earned for the tricks specified in your contract.
If you are vulnerable (vul) and bid and make "game" you will be awarded a bonus of 500 points as well as additional points for all the tricks you win.

Doubling

Doubling adds extra bonuses or penalties whether you are vulnerable or not, the difference is the amount of points you or the opposition are awarded.

You are doubled for penalties and you make your contract with overtricks!

Sometimes the partnership doubling for penalties gets it all wrong and the declarer not only makes the contract they make it with overtricks. For these overtricks when doubled massive amounts of bonus points are earned.
For each doubled overtrick, non vulnerable = 100 points
For each doubled overtrick, vulnerable = 200 points

How to determine which pair/s are Vulnerable or Not Vulnerable

West, North, East and South are all Vulnerable (red )

All positions  are Not-Vulnerable (grey)

North & South are Vulnerable; East & West are Non-Vulnerable

West & East are Vulnerable; North & South are Non-Vulnerable