In making custody decisions based on the best interests of a child, courts look to following factors,

Many divorces involve more than figuring out which spouse gets what property and if and how much one spouse must pay the other in alimony. Often, divorcing parents have disagreements about who should have custody of their children, and like many other divorce issues, it's usually up to the court to settle the dispute.
The gold standard of any custody decision is what custody arrangements best serve the interests of the child. A determination of what's best for any particular child requires a case-by-case examination of both the needs of the child and the advantages presented by those seeking custody.

Custody Disputes

Obviously, most custody disputes involve a mother and father at the time of or after a divorce. Occasionally, a custody dispute arises when the parents have never been married. Sometimes, custody disputes involve third parties, usually relatives, seeking custody at the time of the death or incapacity of a parent.
The courts approach these situations in pretty much the same way. They start with a presumption that parents are in the best position to look out for the welfare of their own child. This presumption can be overcome by establishing that a parent isn't fit or able to best care for the child.

Factors Courts Consider

In making custody decisions based on the best interests of a child, courts look to various factors, usually set out in the state law or case law.

Factors for Parents

The factors courts look at when it comes to the parents include:

• Which parent is the most suitable custodian based on character, temperament and stability?
• What's the child's relationship with each parent?
• What's the educational level of each parent?
• What child-rearing skills does each possess?
• Does either parent have an illness that may harm the child?
• Which parent will provide the best home environment?
• Does the child have stronger emotional ties to one or the other parent?
• Does the child have special needs that can be better met by one parent over the other?
• With whom has the child been living on a regular basis?
• What type of extended family relationships exist?
• What's the employment status of each parent?
• What's the financial status of the parties?
• What's each parent's apparent motive for seeking custody?
• Is either parent unfit to have custody? (Drug or alcohol abuse, for example, usually makes a parent "unfit")
• Which parent is the most likely to allow the child a meaningful relationship with the other parent and extended family?
• The ability and interest of each parent to provide for the emotional, social, moral, material and educational needs of the child

These factors are not exclusive. A court may also look at where each parent lives, the local school system or a parent's other relationships. While being unfit to have custody is an automatic disqualifier, the remaining factors are not given the same weight in each case.
A parent seeking custody can't just look at all the factors, put a check mark in each column where it weighs more in favor of one than the other and then total up the scores. Judges give different weight to each factor in each case.

Factors for the the Child

Some states have lists of factors that focus on the child, rather than the parents, when making a custody decision. Courts may look at some or all of these factors:

• The sex and age of the child
• The child's emotional, social, moral, material and educational needs
• The respective home environments offered by the parties
• The interpersonal relationship between each child and each parent
• The interpersonal relationship between each child
• The effect on the child of disrupting or continuing an existing custodial arrangement
• The preference of each child, if the child is of sufficient age and maturity
• The report and recommendation of any expert witnesses or other independent investigator
• Available custody alternatives
• Any other relevant matter the evidence may disclose

Here also, judges give different weight to each factor on a case-by-case basis.