Hope this helps. The following comes from the web site for Depo Provera Patient Prescribing Information:

"Return of Fertility

Because DEPO-PROVERA Contraceptive Injection is a long-acting birth control
method, it takes some time after your last injection for its effect to wear off. Based on the results from a large study done in the United States, of those women who stop using DEPO-PROVERA Contraceptive Injection in order to become pregnant, about half of those who become pregnant do so in about 10 months after their last injection; about twothirds of those who become pregnant do so in about 12 months, about 83% of those who become pregnant do so in about 15 months, and about 93% of those who become pregnant do so in about 18 months after their last injection. The length of time you use DEPO-PROVERA Contraceptive Injection has no effect on how long it takes you to become pregnant after you stop using it."