Do you want to stay longer in Mexico, but your tourist card is about to expire? Mexican immigration officials decide how long to give you when you enter Mexico, but if you were granted less than six months, you may be able to extend your stay. You will have to visit the immigration office and complete some paperwork in order to stay in the country legally, however.
About Mexico Tourist Cards:
As a tourist in Mexico, you must have a valid tourist card (FMT).
The time period given on your tourist card is at the discretion of the immigration officer who issues it, but the absolute maximum time is 180 days. If you were granted fewer than 180 days when you entered Mexico and you would like to stay longer than the time allotted on your tourist card, you will need to extend your tourist card.
How to Extend Your Tourist Card
Visit the nearest Mexican immigration office. Here is a list: Offices of the Instituto Nacional de Migracion.
You will be asked to show your passport and valid tourist card, as well as proof that you have sufficient funds to support yourself during your stay in Mexico (credit card or bank card, traveler's checks, and/or cash).
You will need to fill in the form you are given in the immigration office and take it to the bank to make a payment, and then return the forms to the immigration office.
Make sure to get there early enough to complete the whole process (including possibly long line-ups at the bank and immigration offices).
Immigration office hours are Monday to Friday 9 am to 1 pm, closed on national holidays.