Unfortunately, that doesn't work!
There are going to be times when you can't do your 50% (like when sick or 9 months pregnant). When you expect your spouse to give 50%, you will grow resentful when it doesn't happen. You will be busy keeping score instead of even keeping up with your 50%.
A marriage will be successful if both spouses give 100%. If each spouse does the best he/she can do, then it fills in the gaps and supports the other in time of need. Even if one spouse isn't giving 100%, the love and actions of the other spouse doing so can have major positive reactions.
1 John 3:18
My little children, let us not love in word, neither in tongue; but in deed and in truth.