How much income should I have to sponsor my parents to the US if I am a 36 year old single?

The required amount of documentable income necessary to meet the requirements for an Affidavit of Support in a family-based immigration application depends upon such things as the applicable family size and geographical location. A chart showing the relevant information may be found here: https://www.uscis.gov/system/files_force/files/form/i-864p.pdf As you can see, for most people the applicable amount of documentable income for a single person sponsoring two parents is $25,525. If the U.S. citizen relative does not have sufficient documentable income, it may be necessary to have a joint sponsor for the application process. Generally a joint sponsor may be any U.S. citizen or Permanent Resident who has sufficient documentable income and who is willing to assume the responsibilities contemplated in the Affidavit of Support. The application process can be more complex than it may appear just from reading the immigration-related forms, their instructions, the statute and the regulations. It would be wise for you and your parents to consult with an immigration attorney who, after learning all of the relevant information about your family, could advise about eligibilities, options and strategies and then could offer legal representation in the application process.