The COVID-19 pandemic has highlighted that access to timely health spending data is crucial for informed policy-making. This Health Working Paper summarises and compares the methodologies applied in around half of OECD countries to estimate public and private health spending for the most recent year (i.e., t-1) as well as the approaches taken by the OECD Secretariat to fill existing data gaps for the remaining OECD countries. For the first time, the paper also explores the feasibility of nowcasting health spending for the current year (i.e., t) and examines data sources that could be potentially useful in such an exercise. While this review should help OECD countries that do not yet have experience in estimating health spending for year t-1 to improve the timeliness in their data reporting, the paper also analyses the applicability of the methods in low- and middle-income countries.