once you have delayed the payment, the months are counted like this (eg)
lets say TDS was deducted in January 2014 (lets say 15 January)
The due date was 7th Feb. if the TDS is not deposited by 7th feb, and paid on 20th march. then you need to pay interest for three months. 1. part of january counted as one month, 2. full february and 3. part of march as one month.