Background: The economic cost of not breastfeeding in Indonesia is estimated at US1.5–9.4billionannually,thehighestinSouthEastAsia.Halfofthe33.6millionworkingwomenofreproductiveage(WRA)inIndonesia(15–49years)areinformalemployees,meaningtheyareworkingascasualworkersortheyareself−employed(smallscalebusiness)andassistedbyunpaid/familyworker(s).NospecificmaternityprotectionentitlementsarecurrentlyavailableforWRAworkinginformallyinIndonesia.Thisstudyaimstoestimatethefinancingneedofprovidingmaternityleavecashtransfer(MCT)forWRAworkingintheinformalsectorinIndonesia.Method:ThecostingmethodologyusedistheadaptedversionoftheWorldBankmethodologybyVilar−Compteetal,followingpre−setstepstoestimatecostsusingnationalsecondarydata.Weusedthe2018IndonesianNationalSocio−EconomicSurveytoestimatethenumberofwomenworkinginformallywhogavebirthwithinthelastyear.Thepopulationcovered,potentialcashtransfer’sunitarycost,theincrementalcoverageofthepolicyintermsoftimeandcoverage,andtheadministrativecostswereusedtoestimatethecostofMCTfortheinformalsector.Result:At100175million (US152/woman)toUS669million (US$583/woman). The share of the yearly financing need did not exceed 0.5% of Indonesian Gross Domestic Product (GDP). Conclusions: The yearly financing need of providing MCT for eligible WRA working in the informal sector is economically attractive as it amounts to less than 0.5% of GDP nominal of Indonesia. While such a program would be perceived as a marked increase from current public health spending at the onset, such an investment could substantially contribute to the success of breastfeeding and substantial corresponding public health savings given that more than half of working Indonesian WRA are employed in the informal sector. Such policies should be further explored while taking into consideration realistic budget constraints and implementation capacity