What is each individual’s budget
Each individual should disclose their financial information, such as their salary, personal expenses, any debt that they may have etc. This way the couple will have a pretty good picture of the family budget and then they can decide whether they will be dividing expenses in half or according to their incomes or other agreed criteria. In practical terms this means that both individuals should be well aware of the fixed and non-fixed expenses of the house and that they should both participate in the financial decisions concerning the house.
What about their savings?
It is often the case that one partner is not aware of the other partner’s savings. Secrecy around something this important is not a wise tactic. If the truth comes out, and it is different to erstwhile assumptions, it could cause a lot of problems. A solution for the couple may lie in opening a joint savings account or setting up a savings program where both partners would have access and equal rights. Whether any existing savings will be included in the above is a decision that should be made jointly.

How to manage money
How a person handles money and his financial habits can vary significantly from one person to another. The couple should have an honest conversation about this subject. One solution could be to set up a shared savings fund or account, while maintaining independence of course on the level of each partner's expenses.
Scripta manent
Surely cohabitation isn’t a commercial transaction. However, it would be prudent, to treat certain issues as such. In other words, whatever is agreed among the couple, depending on the gravity, it would be best to have it in writing, in order for both sides to be secured and to be able to refer to it if necessary.
Cohabitation always presents challenges, no matter how loving or well matched a couple may be. Being crystal clear about the financial issues can help avoid potentially awkward or difficult situations and reinforce harmonious cohabitation.
Sources:
Eurostat, When do young Europeans leave their parental home?
Western & Southern Financial Group