This gives you until October 15 to file without penalties. An extension is granted for filing the return only.Payment of the estimated tax due must accompany the request for extension of time for filing the return. Easy to Request a Tax Extension. IRS e-file is the IRS's electronic filing program. An extension gives you up to six months to file or up to Oct. Applying for a STEM OPT extension. To apply for an extension, you must file: Form I-765 (including the application fee). Filing an extension gives you extra time to efile the return. OISS will review the application, recommend OPT STEM.