OBJECTIVES: To determine acceptability and feasibility of human capital and willingness-to-pay approaches, estimate indirect and intangible costs of knee OA using these approaches, and identify factors potentially affecting these costs in Singapore. METHODS: Data were collected through face-to-face interview among knee OA patients. Human capital approach was used to estimate indirect costs by multiplying: 1) days of absence from work due to OA with average gross earning per capital per day for working patients, or 2) productivity loss with the market price of housekeeping and leisure activities for homemakers/retirees. A closed-ended iterative bidding contingent valuation method was used to elicit willingness-to-pay for a hypothetical cure of OA as a proxy for intangible costs. Mann-Whitney U or Kruskal-Wallis H tests were performed in univariate analysis, and linear regression in multivariate analysis. RESULTS: Indirect costs per year and intangible costs were estimated at US$1008 and US$1200, accounting for 2.8% and 3.3% of annual household income, respectively. The indirect costs were significantly higher for male or working patients, while intangible costs were higher for Chinese, working patients, patients with higher income, or worse global wellbeing. CONCLUSION: This study indicated that both human capital and WTP approaches are acceptable and feasible methods in eliciting indirect and intangible costs which are substantial for patients with knee OA in Singapore. Most importantly, a congruence in the magnitude of indirect costs relative to annual household income was observed across countries, which implies that it may be possible to provide a “standard reference range” of indirect costs for economic evaluation for various diseases.