What the calculator uses
The pass recommendation is driven by the trip window and the current JR Pass price table. The trip window is the date range from your first departure to your last departure, inclusive.
For the route side, the page uses a maintained city-hub dataset and a deterministic fare estimator. That keeps the result stable, inspectable, and easy to refresh when the underlying fare tables change.
Supported hubs currently include Tokyo, Kyoto, Osaka, Kobe, Nagoya, Hiroshima, Hakata, Sendai, Morioka, Aomori, Niigata, and Kanazawa.