Lag when win.blit() background pygame

Solution 1:

Ensure that the background Surface has the same format as the display Surface. Use convert() to create a Surface that has the same pixel format. That should improve the performance, when the background is blit to the display, because the formats are compatible and blit do not have to do an implicit transformation.

bg = pygame.image.load('images/bg.jpg').convert()

Furthermore, it is sufficient to create the font once, rather than every time when a text is drawn. Move font = pygame.font.SysFont('Comic Sans MS', 25, True) to the begin of the application (somewhere after pygame.init() and before the main application loop)