If it's a wife or you have a child together, then yes. But if it's a girlfriend, I think it's okay to split 50/50. Perhaps cultural background also plays a role in this decision. Personally, I cover 70% of the expenses while my girlfriend contributes 30%. I wouldn't want her to bear the entire financial burden, but at the same time, I wouldn't want a woman who is completely dependent on me financially - unless of course, I am a millionaire!