If you fail to pay your monthly NHIF payments or pay late you accrue a penalty of Ksh 250/= per month, which must be paid at any of these branches; Kenya Commercial Bank, Equity Bank, National bank and, Cooperative bank. Please note that the penalties have to be paid at the bank branches and not the agents.) In addition, you will also pay the premiums, which is Khs 500 for every month missed. The premiums can be paid via Mpesa .NHIF Mpesa pay bill number is 200222 and the account number is your Id number.
You can contact NHIF via their Twitter handle @nhifkenya for a quick response if you have any query regarding your late payment.