Two working couples:

- Two incomes

- Shared health plan (more expensive but less than 2x single?)

- Shared apartment (more expensive to support two occupants but less than 2x single?)

- Opportunities to reduce duplicated expenses when possible: e.g. single set of furniture, single car, joint loans (e.g. mortgage + closing costs), repairs, etc.

If one of the partners is not working I believe there are still advantages but they might be harder to quantify. Even if it means cutting out one of the incomes, having a time-available partner can be advantageous in other ways. Time to cook vs. eat out (more cost effective), organize bills, find discounts and deals (e.g. credit card churning for saving ~1k-2k a year on flights), organizing activities to maintain health, arrange doctor visits for preventative care, etc.

Obviously, this equation changes when one is a dependent but if both are independent and work together I feel that the math would favor couples.

[0] https://www.theguardian.com/law/2015/mar/11/woman-wins-right...