We have estimated under-reporting of coronavirus until March 9, 2020, in various countries until the first peak occurred in each of the countries that have reported 500 or more cases of COVID-19 as of March 9, 2020. Our retrospective model-based estimations of under-reporting (including those due to under-diagnosis) will be helpful in the assessment of pandemic preparedness required. The ratio of reported COVID-19 cases to model-based predictions of COVID-19 for eight major countries who have reported 500 or more cases up to March 9, 2020, were provided.