Very common, and usually workable. What makes it work is deciding deliberately rather than drifting, and being honest about who is paying what.
The usual arrangement
In most mixed households the kitchen follows the more stringent practice. Not because that person wins, but because it is the only arrangement under which both people can eat at home together. A partner who keeps kosher cannot eat in a kitchen that is not; a partner who does not keep kosher can eat perfectly well in one that is.
So the practical default is: the home is kosher to the standard the more observant partner needs, and the less observant partner is not personally obliged by it but lives inside it.
That arrangement is workable for a large number of couples. It has a cost, and the cost falls on one side, which is the part that needs saying out loud.
What actually needs deciding
The kitchen. What standard, exactly. Kosher-style, certified meat, separate dishes, separate sinks, full supervision — these are quite different arrangements with quite different demands.
Outside the home. Whether the less observant partner eats non-kosher food elsewhere, and whether that is genuinely fine with the other one. Many people say yes at the start and find later that it bothers them more than expected. Ask twice.
What comes into the house. Takeaway, food brought by guests, what happens on holiday. The details are where the actual arguments are.
Guests and family. Whether the less observant partner’s family can host you, and what happens if they cannot host to the standard required. This is a live source of hurt feelings and is better negotiated in advance.
Children. What they are taught, what they eat outside, and what the rule is when they are old enough to choose.
What is not for the couple to decide
An important distinction. Whether you want a kosher kitchen is a decision. What a kosher kitchen actually requires is not — it is a question of halachah, and the answer differs between authorities and communities.
Couples routinely turn this into an argument about reasonableness when it is a question with an answer. If you are setting up a kitchen together, ask a rabbi in the relevant community what is actually required, and make the decision with the real answer in front of you.
“How strict do we need to be?” is a question for a rabbi, not a debate between two people with different intuitions. Getting the actual requirements first tends to shorten the conversation considerably — and it removes a recurring source of argument about whose standard is arbitrary.
The resentment pattern
The thing to watch for is accumulated, unacknowledged cost.
The less observant partner has given up food they liked, restaurants they used to go to, ease when travelling, sometimes the ability to eat at their own parents’ table. The more observant partner has given up nothing and may not have noticed there was a cost at all.
That does not have to be equal. It does have to be seen. Couples where the observant partner regularly acknowledges what the other is doing do markedly better than couples where it is treated as simply how things are.
The reverse pattern also exists: a partner who agreed to a kosher home and then erodes it in small ways, which the observant partner experiences as a promise being quietly withdrawn.
The question underneath
Ask it directly before you marry: are you agreeing to this, or accommodating it?
Agreeing means you want this home. Accommodating means you are doing it for them. Both can work — but accommodating has a shelf life unless it is recognised, and the person doing it should know that about themselves.
And then the other one: are you hoping I will change? An honest yes can be worked with. An unspoken yes is the thing that surfaces as an argument about a saucepan in year six.