Background: Exertional desaturation is an important marker of disease severity in people with fibrotic interstitial lung disease (fILD). The 6-minute walking test (6MWT) is used to identify exertional desaturation and justify the prescription of ambulatory oxygen therapy (AOT). It is unclear if it reflects daily desaturation in patients with fILD. Aim: To compare exertional desaturation during 6MWT and during daily life in patients with fILD. Methods: Participants performed two 6MWT and underwent home oximetry during waking hours for two consecutive days. The relationship between 6MWT exertional desaturation and daily desaturation was evaluated. The impact of physical activity (steps per day) on daily desaturation was also assessed. Parametric tests, Pearson?s correlation coefficients and multiple linear regression analysis were used. Results: Eighty-two people with fILD were recruited and 58 recordings were analyzed. Participants had moderately severe lung disease and low physical activity. The 6MWT nadir SpO₂ was higher than daily minimum SpO₂ (82 ± 4% vs 75 ± 5%; P< .001). Lower daily SpO₂ correlated with shorter 6MWT distance [P= .036], lower 6MWT nadir SpO₂ [P= .019] and fewer steps per day [P = .025). The number of steps per day (? = 0.001; P = .045) and 6MWT nadir SpO₂ (? = 0.31; P = .027) were independent predictors of daily minimum SpO₂. Conclusion: The 6MWT can accurately identify exertional desaturation in people with fILD but, may underestimate its extent. Lowest daily SpO₂ may be predicted by 6MWT nadir SpO₂ and physical activity, parameters that should be considered for AOT prescription.