The calculation of spousal support or alimony is judged based on the parties’ circumstances and their needs and abilities to pay. Some of the factors that the court may consider in determining spousal support include the earning capacity of each party, their age and health, their needs, and their assets and liabilities. And support obligations that did not arise out of the current marriage are considered as debts incurred before marriage.

California Family Code 915.(a)

a child or spousal support obligation of a married person that does not arise out of the marriage shall be treated as a debt incurred before marriage, regardless of whether a court order for support is made or modified before or during marriage and regardless of whether any instalment payment on the obligation accrues before or during marriage.” (Emphasis added)

So many other factors may be considered for the computation of alimony, and the best thing to do is to consult and work with a lawyer who is an expert in divorce and family law.