The easiest way to figure out how much, if any, child support would be paid would be for you to go to the County-City Building Law Library (it's in the first floor) and they have a computer program that's free for you to use (except you pay for any pages you actually print). It's called SupportCalc. You can plug in the incomes and other factors specifically for your case and see what comes up. It has a specific option to calculate based on how many overnights a parent has.
Very very generally speaking, child support is figured with the two kids and the the paying parent is given a residential credit for the amount of time that the kids spend with him/her.
I strongly recommend that you fiddle around with SupportCalc. Courts will usually adopt whatever SuportCalc spits out.
In Washington, child support is based upon mandatory Child Support Schedules. This determines the basic amount of the transfer payment. From this, the court can deviate the amount if there is a legal basis for it. One reason for deviation is a residential credit. If the children spend a significant amount of time (usually considered to be more than 90 overnights a year) with the non-residential parent, then the court can reduce the amount of the transfer payment. There is a formula that has been used for years to calculate the amount of reduction, but last year the appelate court struck down the formula approach. You can still calculate the formula for your own reference or agreement, but the court will not strictly follow it. Now we are left to prove to the court the added expenses for the non-residential parent who has them for more time, and the reduction of expenses for the residential parent who has them for less time. This is a much more difficult task than just putting the number of overnights into the formula.
If you share custody equally then the issue of child support is discretionary with the court. This is an interesting situation because in an analgous situation, where each parent has primary care of one of two children of the marriage, our appellate court in a case called Marriage of Arvey havs provided a specific formula for how to calculate support. When the parties share time with children equally you would think the Arvey formula would also apply because it is conceptually the same as each parent having one child. In any event, the way you should do it in your case is to designate the parent with the larger income as the majority parent or obligee parent. Then utilize the residential credit available on most computer programs and tabulate the number of overnights for the obligor parent--which should be one half of 365 since you share time equally. The computer program will then compute the support that is owed taking into consideration that there is shared custody. It is still discretionary with the courts but most of the time they will deviate in this way when the parties share residential time with children.
Sign up to receive a 5-part series of useful information and advice about child custody law.