The exam dates for classes and entrance tests usually start from middle of March and go on till May depending on your board or exam type, for example state board exams begin around 15 March and finish by early April, while entrance exams like engineering or medical start from 1 April to mid May, schools also plan internal exams in February or March before annuals start, after that exam schedule comes online and students get time table from school or portal, colleges and universities announce dates two or three months before, so to know exact date for your exam you check official board or college portal, but as common pattern exam season is March April May, full list of dates and exam calendar can be seen here

https://school.careers360.com/articles/school-exam-calendar