Armour layering and penalties is a topic that keeps confusing new players. This guide is a supplement to the armour calculator, that explains the underlying process step by step in more detail.

When wearing any number of armour pieces, the resulting armour and penalties are determined as follows:

1. Add up the ratings of all matching set pieces you're wearing, and round DOWN. The set is treated as a single piece of that rating. Wearing pieces from multiple sets is not supported and will break this functionality.
2. Determine what the single best worn piece is, counting the total ballistic + impact armour value. This piece is counted for 100% of its value both for purposes of armour value and penalties (unless it happens to be a form-fit piece, in which case it's not counted for penalties). If you have several pieces with the same ballistic + impact value, the MUD seems to prioritize the higher ballistic piece.
3. Add up the ratings of ALL other worn pieces with an armour rating, INCLUDING form-fit, divide by two and round down. This value is added to the armour ratings.
4. Add up the ratings of the same pieces as in stage three EXCEPT form-fit. This value is added to the value used to calculate penalties.
5. Add any bonus values from cyberware, magic, helmets, and forearm guards to the total armour rating (this doesn't affect penalties).

If your penalties value is higher than your quickness, you will experience penalties.

For more info please refer to the ingame files LAYERING, FORMFITTING and “ARMOUR SETS”.