Well, she should be 100% responsible for her two kids. She works and collects CS for them.

You should share the expenses for the infant.

Bills like mortgage, food, utilities, etc should be split by the number of people. Are her kids there 100% of the time?
BTW, this is one of those things that should get discussed before marriage.

Split everything down the middle. We do that and have a credit card for family and household purchases and split it at the end of the month. He pays for the extras for his kid and I pay for mine. Works great for us.

This should have been laid out in your pre-nup.

Whatever you do, keep your checking accounts separate. This avoids fighting about times when she will spend money on skids (overspends I mean) or something you think is excessive. If she spends the money, its on her. Not you.

I understand the her kids my kids concept, but doesn't a HUGE part of marriage mean that you are there to support eachother emotionally and financially? If you or both of you are concerned about who is contributing more, then why not combine your checking accounts and money? Pay bills first, then every purchase after that discuss between the two of you. I realize that no one can love someone else's kids as much as they do their own, but you can support them as a team. If you don't combine your finances then the person who makes less is always going to feel like they aren't part of that equal team.

I have 2 kids, my FDH has one. I pay all utilities and food. He pays the mortgage (we figured that worked out close to equal, I pay probably $100 more but that is because I refuse to buy crappy food) and then we pay our own individual bills (child care for our kids,cell phones, taxes, credit cards, student loans). When it comes to purchases for kids I usually pay everything up front and he pays me right back. It works for us, I haven't had a problem yet. But we communicate and discuss any bigger purchases. That way he is never caught off guard and we can both budget for expenses.

My situation is different because we have a his and mine situation, no ours. I would say split the "our" kid cost for clothes, daycare, sports, etc when it comes time and try to keep the household budget close to equal but her pay a little more. If she works I am sure that a big bulk of her CS goes to daycare costs, I know the CS I get almost all goes to that.

I wish you could have talked about this before you got married. Money is such an uncomfortable topic.

My SO don't live together yet, but we've had this very uncomfortable discussion. Basically, we decided that we'd each contribute a set amount to a joint account and that's what we'd pay household bills out of. Basically, I'd contribute 65% of the household money and he'd contribute 35%. That would cover mortgage, water, gas & electric, cable/satellite (not that we have it but if we did), home phone (if we choose to have one) and a set amount for household groceries ($100 a week).

Then we'd have our own accounts to put the rest of our money in and do with what we needed to - pay for our cellphones, kid specific things, child support for his kids, etc.

Considering right now he makes about 45% of what I make, but he pays out just as much in mortgages nad other bills as I do - this works out for both of us and having been severely screwed over financially in the past, I can not just go all in while we have under age children and his exwife is insane.

My dh always says just pay my cs with your cs....umm NO! we have a combined checking account but I'm not comfortable taking money off my cs card and paying his with it. I don't know why maybe it's a thing of mind over matter but it doesn't feel right. I will pay household bills with my cs but never his cs!

I lived in her home and paid her as if I was a roommate getting room and board. A fixed amount based on local market for roommates.

She the paid everything about the home. When my kids came over for a weekend I paid for the extra food purchased.

Often I took wife and her kids out to eat and paid as a bonus so to speak and occasionally rescued her when her car broke down.

A mutual child did not enter into the picture.