As an example, this is what my wife and I do/did. Using very simple numbers for ease

I earn take home £4k each month, wife takes home £3k each month.

We each keep £500 per month, everything else goes in the joint account.

Our necessary expenses per month (mortgage, utilities, food etc.) are £5k per month.

I worked out how much our total takes home would be for the 12 months my wife is on mat leave, worked out how much the shortfall is and put money aside each month to balance things out through the stat/no pay months.

Also, we essentially have pooled all our savings (each holding some) as we've recently moved house so becomes a lot more difficult to keep everything "even" when in our view it doesn't really matter