Count present pieces, not construction history
Each settlement is one point and each city is two. When you upgrade, remove the old settlement from your count. Three settlements and two cities therefore make seven visible points. Adding one victory-point card makes eight total. Upgrading one of those settlements changes the inputs to two settlements and three cities, adding one net point.
Awards are held, not accumulated
Longest Road and Largest Army are worth two points each while you hold them. Enter an award only after its ownership is resolved. Losing an award removes those points; previously qualifying for it does not make the points permanent. The tool does not determine the longest connected road or count played knights.
A total is not a victory declaration
The base game ends when you have at least ten points on your own turn. Hidden victory-point cards contribute to your own total; do not guess an opponent's cards from their purchases. Other formats can have different victory targets, including some Colonist modes. Use the result as a planning checklist for base Catan or Settlers of Catan, rather than a replacement for the rules at your table.
Rules, assumptions & further reading
Check the official CATAN rulebooks and Colonist’s base-game rules for the rules at your table. These calculations and worked examples are original mathematical models, not measured win rates. They do not read a live game or establish that a move is legal.