OBJECTIVES Cost is considered one of the major barriers to greater use of LARC (Long-Acting Reversible Contraceptive) methods, especially cost of treatment initiation. However, when considering their contraceptive efficacy alongside cost of pregnancy, LARC methods are deemed by NICE to be more cost-effective than combined oral contraceptive pills even at one year of use. (NICE LARC CG30 2005). METHODS A 3 year time-horizon cost-benefit model was developed to assess budgetary impact of increasing LARC uptake (implant, IUD, IUS and injectable) compared to the oral contraceptive pill, in UK women aged 16-49 who currently use the following contraceptives of interest: non-LARC method (defined as contraceptive pill only) or LARC methods (IUD, IUS, injectable, implant). A weighted-average price based on current market shares was calculated, for all contraceptive pills currently available in the UK. Increased uptake of any LARC method was offset against a reduction in contraceptive pill usage. Unintended pregnancies, based on typical failure rate, occurring with all treatments considered was taken into account. RESULTS Of approximately 14,750,000 women aged 16-49 in the UK, official statistics confirm 37% use contraceptive methods of interest to our model. This proportion formed our cohort of approximately 5,500,000 UK women aged 16-49, which was followed over a 3 year time horizon. A 100% increase in uptake of each LARC method would lead to a 49% decrease in oral contraceptive pill uptake. Over a three year period this would save 374,794 unintended pregnancies, and elicit financial savings of £630,831,022, on which £54,098,847 is attributable to treatment costs (ingredient, consultations, removal/insertion costs) and £576,732,175 to the cost of unintended pregnancies (live birth, miscarriage, abortion, ectopic pregnancy). CONCLUSIONS