Ramadan fasting has recently resulted in fasts exceeding 19 hours in daily duration. This study examines the sociodemographic correlation of health-related incompletion of Ramadan fasting, hypothesising that longer fasting times and more demanding lifestyles increased health-related incompletion of Ramadan fasts. \ud \ud A cross-sectional study of mature Muslims deemed religiously eligible to fast was conducted utilising an electronic self-completed questionnaire in Ramadan (July) in Great Britain in 2015. The main outcome measure was missing at least one fast due to self-reported health reasons, excluding menses, pregnancy, breastfeeding, or travel related incompletion of fasts. \ud \ud Analysis of 1,973 completed responses revealed that correlates: female sex (compared to males: AOR (adjusted odds ratio) 1.71, 95% CI (confidence interval) 1.31-2.24), reduced religiosity (e.g. least religious compared to most religious: AOR 8.67, 95% CI 3.89-19.30), increased intensity of daily activity (most active compared to most sedentary: AOR 1.89, 95% CI 1.21-2.93), reduced length of fast (fasting 20 hours per day: AOR 2.76, 95% CI 1.29-5.87), having a comorbidity (AOR 3.73, 95% CI 2.45-5.67), and taking medication (AOR 4.92, 95% CI 2.50-9.69) were all significantly associated with missing at least one fast due to self-reported health reasons. \ud \ud Fasting a longer fast (17-20 hours, or >20 hours) was not significantly associated with incompletion of one fast due to health reasons. An increased intensity of daily activity proved to be significantly associated with incompletion of one fast due to health reasons. Further validated research is crucial in developing this evidence base.