The calculated distance (air line) between Karlovy Vary and Mladá Boleslav is approximately 90 miles respectively 146 kilometers.
By car or train, the actual journey to Mladá Boleslav is certainly longer, as only the direct route (as the crow flies) between Karlovy Vary and Mladá Boleslav has been calculated here.
Air line (approximately)
146 kilometers
79 nautical miles