I called up the Mumbai office and clarified the interest on Maharashtra Labour Welfare Fund. As per the rules for June, one needs to pay the contribution charges before 15th August. From 16th August, you need to pay an extra 1.5% for the next three months "each". After three months, you need to pay an extra 2% on all the above charges on a monthly basis. For example, I'm paying the June '17 contribution in January '18. In this case, the contribution amount x 1.5% for the 1st month after 15th Aug, i.e., 16th Aug to 16th Sept is 1.5%. The 2nd month, from 16th Sept to 16th Oct, is + contribution amount + 1.5% of August x 1.5%. The 3rd month, from 16th Oct to 16th Nov, is contribution amount + earlier interest amount of two months x 1.5%. The 4th month, from 16th Nov to 16th Dec, is contribution amount + interest of 3 months x 2%. The 5th month, from 16th Dec to 16th Jan, is contribution amount + earlier interest of 4 months x 2%. That is how you need to calculate the interest and pay. Hope that suffices the query in case anybody has.