Investing in maternity protection for working women is an important social equity mechanism. Addressing the maternity leave needs of women employed in the informal sector economy should be a priority as more than half of women in Latin America, South Asia, and sub-Saharan Africa are employed in this sector. To develop a costing methodology framework to assess the financial feasibility, at the national level, of implementing a maternity cash transfer for informally employed women. A World Bank costing methodology was adapted for estimating the financial need to establish a maternity cash transfer benefit. The methodology estimates the cash transfer's unitary cost, the incremental coverage of the policy in terms of time, the weighted population to be covered, and the administrative costs. The 6-step methodology uses employment and sociodemographic data that are available in many countries through employment and demographic surveys and the population census. The methodology was tested with data for Mexico assuming different cash transfer unitary costs and the benefit's time coverage. The methodological framework estimated that the annual financial needs of setting up a maternity cash transfer for informally working women in Mexico ranges between US$87 million and US$280 million. A pragmatic methodology for assessing the costs of maternity cash transfer for informally employed women was developed. In the case of Mexico, the maternity cash transfer for women in the informal sector is financially feasible.