Hello, i think "Đủ" means "Enough, it is a enough number for (doing) something " and "Đầy đủ" means "Full (of) - nothing is missing according to the requirements" For example you say: "Tôi có đủ (tiền) để xây nhà" means "I have enough (money) to build a house" "Tôi có đầy đủ (dụng cụ) để xây nhà" means "I have full of tools to build a house" Or another "Tôi sống đủ" - I have enough to live (but I might need to thing else to make me happier) "Tôi sống đầy đủ" - I have everything I need to live" (and I don't need more) The differences between those are just slightly because in general it all means "enough". I hope you can understand what I've explained. Good luck ;)