What is in the base development deck?
The base deck has 25 cards: 14 knights, five victory points, and two each of Monopoly, Road Building and Year of Plenty. The default asks for at least one victory-point card in three draws from that full deck. Buying development cards costs ore, wheat and sheep; paying does not guarantee the card you want.
Why three purchases are not three times the odds
The default chance is 1 − (20/25 × 19/24 × 18/23), about 50.4%. Each miss changes the next draw's pool. The expected number of victory-point cards is 3 × 5/25 = 0.60, which is a different quantity from the chance of at least one. The calculator uses sampling without replacement, not repeated independent 20% trials.
Hidden cards stay unknown
Enter a hypothetical pool or counts you can justify. Do not subtract opponents' face-down cards as though their types were known. A pool can include all still-unknown cards only if their locations are exchangeable under your assumptions. Selective purchases, revealed information and unknown deck composition can invalidate a simplified model. This is a scenario calculator, not a live card tracker or a prediction of what another player holds.
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.