Increasing access to effective birth control after childbirth may meet many women's preferences and reduce short interpregnancy interval rates. Eliminating out-of-pocket costs for contraception has been reported to increase the use of the most effective methods among women with employer-based insurance, but the prevalence and effects of patient cost sharing for contraception have not been studied during the postpartum period. This study aimed to examine the association between cost sharing for long-acting reversible contraception and postpartum contraception use patterns and pregnancies in the 12 months after delivery. We conducted a retrospective cohort analysis of commercially insured women undergoing childbirth from 2014 to 2018 using Optum's (Eden Prairie, MN) de-identified Clinformatics Data Mart database. This large national database includes nonretired employees and their dependents who are enrolled in health insurance plans sponsored by large- or medium-sized US-based employers. Women with 12 months of continuous enrollment postpartum were included. Childbirth, pregnancy, and contraceptive method (female sterilization, long-acting reversible contraceptives, other hormonal methods, and no prescription method observed) were identified using claims data. Contraceptive use patterns were observed at 3, 6, and 12 months postpartum and adjusted for individual and plan characteristics. Median out-of-pocket costs were $0 for sterilization and other hormonal methods but nonzero for long-acting reversible contraception. We therefore used simple and multivariable logistic regressions to examine the association between plan-level cost sharing (no cost sharing, $0; low cost sharing, >$0-<$200; and high cost sharing, ≥$200 out-of-pocket cost) for any long-acting reversible contraceptive insertion and contraceptive use patterns and short interpregnancy interval rates, controlling for age, household income, race and ethnicity, region, and insurance plan type. Among 25,298 plans with cost sharing data, we identified 172,941 women with continuous enrollment for 12 months postpartum, including 82,500 (47.7%) in no cost sharing, 22,595 (13.1%) in low cost sharing, and 67,846 (39.2%) in high cost sharing plans. The percentage of postpartum women in the study sample using any prescription contraceptive method was 39.5% by 3 months, 43.8% by 6 months, and 46.0% by 12 months. At all time points, postpartum women in no cost sharing plans had a higher predicted probability of long-acting reversible contraceptive use (eg, at 12 months: no cost sharing, 22.0%; low cost-sharing, 17.5%; high cost sharing, 18.3%; P<.001) and a lower predicted probability of no prescription method use (eg, at 12 months: no cost sharing, 51.8%; low cost sharing, 55.0%; high cost sharing, 54.9%; P<.001) than those in low or high cost sharing plans. Predicted probabilities of female sterilization and other hormonal method use did not differ substantively by plan cost sharing for long-acting reversible contraception at any time point. The proportion of women experiencing a short interpregnancy interval was low (1.9% by 3 months, 1.9% by 6 months, 2.0% by 12 months) and did not differ by plan cost sharing for long-acting reversible contraception at any time point. Out-of-pocket costs for long-acting reversible contraception influence the method of contraception used by postpartum women with employer-based insurance. Eliminating financial barriers to long-acting reversible contraception access after childbirth may help women initiate their preferred method and increase the use of long-acting reversible contraceptives among interested women who otherwise might utilize less effective methods.