I bought an ESTA early this year and I know that I am only granted 90 days within america using one. I wanted to know if this was an allowance or if The 90 days get renewed when I go back to America. For example, if I was to go to america for 17 days and I came home, would I only have 73 days left? or would I have 90 days again?
I know this question is a bit dated, however I thought I'd answer in case you or other travellers need to know in future.
The ESTA is not the same as a visa, it is a pre-visa check which the US requires for foreign visitors wanting to access the Visa Waiver Program. Typically an ESTA, once approved, lasts for 2 years or until the passport you applied for expires. It can be used for multiple entries within that period provided your information/status hasn't changed.
The 90 days from the visa waiver program starts from first entry, but if you went back with a fair buffer time between visits, and an eligible ESTA, it should restart as you would technically be getting a new visa upon arrival.
More information can be found on these sites:
https://travel.state.gov/content/visas/en/visit/visa-waiver-program.html about 3 years ago