Not all states recognize separation agreements. In some places, they go by different names, such as judgments for separate maintenance. In all instances, however, a separation agreement is a comprehensive document meant to address every possible issue between couples who are about to part ways.
You should decide which of you--if not both--is going to be responsible for major decisions regarding your children's upbringing. Set forth which nights the children will reside with each of you. Determine such issues as which parent the children are going to spend significant holidays with and what happens if one parent wants to take them on a two-week vacation.
Child Support/Spousal Support
Most states use child support guidelines to calculate support, basing it upon the incomes of both parties, the ages of the children and the number of overnights they spend with each parent. You should consult an attorney to decide upon how much child support is appropriate in your particular case. Spousal support is trickier. The general rule of thumb is that it is meant to equalize the incomes of spouses now living separately. But there are exceptions to the rule if one spouse is paying some or all of the household bills for the other, so you should also determine appropriate adjustments.
Most auto insurance companies will not insure an automobile that is being garaged at a separate residence. Likewise, health insurance companies will not insure an ex-spouse. This could make legal separation more attractive than divorce, but health insurance companies are becoming increasingly savvy to this trend, so read the fine print contained in your policy. You should also address which parent is going to cover the children and who is going to pay for their uninsured medical costs.
If one of you has sufficient income, you can buy out the other's interest in any property you co-own. This would be half of the differential between the fair market value and any existing liens against the property. If the home is placed on the market for sale, make sure you itemize exactly what is going to happen with the proceeds. Determine how you will divide the funds and whether the funds will be used to pay off or pay down credit card debt.
These can run the gamut from 401(k) plans to pensions and are heavily affected by the duration of the marriage. If a spouse has been paying into a defined benefit plan every week through a 20-year marriage, you should consider that the other spouse has a legal right to some of that. If you have only been married two years, your percentage share of a pension would be minimal. Either way, retirement benefits should be addressed.
You won't need a checklist to remember the big ticket items you bought while you were married. Little things, however, could get lost in the process. You should take a calm moment to walk through your home (preferably alone) and make a list of anything that is important to you, that you brought into the marriage or that was gifted to you.