HIV/AIDS is a major health issue faced by the world, generally, but particularly sub-Saharan Africa. Nigeria ranked third in the world by number of people living with HIV/AIDS in 2019. Despite prominent HIV counselling and testing (HCT) intervention programmes, Nigeria faces serious challenges, such as inadequate funding and low utilisation rates. Paucity of research into such a critical topic has restricted the capacity of policy makers to address the problem adequately. Consequently, a cross-sectional study was carried out using the contingent valuation method to assess the economic quantum of payment and determining factors associated with people's willingness to pay for HCT services. Data were collected from 768 people selected by convenience sampling of three local government areas - Alimosho, Ikorodu and Surulere in Lagos State, Nigeria. Data were analysed using descriptive statistics, chi-square, Mann-Whitney, and general linear regression model analysis. Findings show that 75% of respondents were willing to pay an average fee of N1 291 ($4.22) for HCT services. Significant determinants of willingness to pay were: income; knowledge of someone living with HIV or died of AIDS; worry about HIV infection; and fear of HIV-related stigma. The findings offer vital information germane to co-payment schemes aimed at financial sustainability of HCT and HIV/AIDS programmes in Nigeria.