Before providing an answer to your question, I need to recommend that you consult with an attorney in your area who can answer these questions in greater detail, and as applied to your particular situation. The information contained in this answer is just that: information only. You cannot rely upon it as a legal opinion or advice. The calculation of alimony, or "spousal support" in California is actually somewhat complicated. There are essentially two types of spousal support in California: temporary and permanent. The temporary spousal support refers to the support that is received during the pendency of the litigation. This support is usually calculated pursuant to a formula. In Los Angeles County, the courts employ what is known as the Santa Clara County guidelines. Essentially, the formula calculates 40% of the paying party's net income and subtracts from that number, 50% of the receiving party's net income. The remaining figure is the suggested amount of support.
"Permanent support" is a much more complicated exercise. It involves the consideration of a variety of factors, as are set out in the California Family Code. These factors include (but are not limited to) such things as the health of the parties involved, the length of the marriage, the financial situation of the parties, the marital standard of living, and things of this nature. These factors can be found in section 4320 of the Family Code. Quite literally, volumes of writings have devoted themselves to the analysis of the calculation of permanent spousal support. As such, any attempt by me to do the same here is impossible. As indicated above, I strongly suggest you consult with an attorney who can give you more detailed advice on the subject.
As for how long you can anticipate to receive support, generally speaking (and when I say that I mean that this is not a hard and fast rule, but, rather, is simply the guideline for presentation by the court), if you have been married for less than 10 years, you will likely receive the support for a period of time roughly equal to one half the length of your marriage. If you have been married for more than 10 years, the courts are free to enter whatever calculation they deem appropriate under the circumstances presented by your case.
Unlike child support, which follows the formula set forth in California Family Code 4055, there is no set formula for spousal support. Rather, spousal support in a divorce settlement/judgment is calculated using the factors of Family Code section 4320, such as:
(a) The extent to which the earning capacity of each party is sufficient to maintain the standard of living established during the marriage, taking into account all of the following:
(1) The marketable skills of the supported party; the job market for those skills; the time and expenses required for the supported party to acquire the appropriate education or training to develop those skills; and the possible need for retraining or education to acquire other, more marketable skills or employment.
(2) The extent to which the supported party's present or future earning capacity is impaired by periods of unemployment that were incurred during the marriage to permit the supported party to devote time to domestic duties.
(b) The extent to which the supported party contributed to the attainment of an education, training, a career position, or a license by the supporting party.
(c) The ability to pay of the supporting party, taking into account the supporting party's earning capacity, earned and unearned income, assets, and standard of living.
(d) The needs of each party based on the standard of living established during the marriage.
(e) The obligations and assets, including the separate property, of each party.
(f) The duration of the marriage.
(g) The ability of the supported party to engage in gainful employment without unduly interfering with the interests of dependent children in the custody of the party.
(h) The age and health of the parties.
(i) The immediate and specific tax consequences to each party.
(j) The balance of the hardships to each party.
(k) The goal that the supported party shall be self-supporting within a reasonable period of time. A "reasonable period of time" for purposes of this section generally shall be one-half the length of the marriage. However, nothing in this section is intended to limit the court's discretion to order support for a greater or lesser length of time, based on any of the other factors listed in this section and the circumstances of the parties.
(l) Any other factors the court determines are just and equitable.
This is for purposes of settlement and judgment. If you are talking about pendente lite (temporary) orders, other factors will be reviewed.