I am a British citizen with an F1 visa. I am currently employed as a full time permanent employee under the OPT allowance, while my employer applies for an H1B on my behalf.

What taxes am I exempt from while still on the F1?

Many thanks,
Debora

Debora:

The key is your H1B visa status.

The day your H1B visa goes into effect is the day you become liable with Social Security and Medicare taxes.

Until then, you are exempt from these taxes.