When shld you tell your boss about pregnancy?

i inform my boss next day after i know im pregnant... as i working as retail line... i need to carry stock,climbing up and down the ladder to take stock... then they can arrange my working schedule for not working too much full shift etc.. so to fair and safe. So just incase u need to go for checkup and take maternity leave as they need to plan for the manpower to cover you incase anything.