Do I file I-134 or I-864a? Would it be 100 percent or 125%

For a K-1 visa, you would file an I-134 affidavit of support since this is a nonimmigrant visa. If your mother is living with you, you could perhaps adapt the form to include both of you for the support. If your mother is living apart, she could perhaps file another I-134 form. After your fiancé is admitted to the States and you are married, an I-864 affidavit of support will be required for the adjustment of status. You would have to fill it out, and your mother could join in with an I-864A supplement if living with you. If not, she would be filing a separate I-864. If your mother files her taxes as married, she would likely have to include the spouse in the count of the number of people in her household. An I-134 is judged at 100% and an I-864 125% of the poverty guidelines.  I do note that although the above are the rules, we have sometimes been surprised by a consulate asking for an I-864 for K-1 processing, so it may be safer to prepare both.Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.