The information on the Thai Immigration website still states that a minimum of three months is needed: https://www.immigration.go.th/content/service_22
Recently though, statements have been made that contradict this information and now its suggested that 12 months proof of funds is going to be the requirement but not enforced until the end of Dec 2019.
Thai immigration say that they’re willing to show leniency to foreigners in the prickly subject of proving income when applying for retirement and marriage visas and extensions.
General Surachete Hakparn
Immigration chief Police Lieutenant General Surachete Hakparn acknowledges that some applicants may have difficulty in providing the now required 12 months worth of bank statements.
Where this is the case Surachete has instructed immigration officers that, up to the end of 2019, they will have discretion to accept evidence of less than 12 monthly transfers from overseas.
Applicants given leniency in this case are being told that this is a one-off exemption and that their applications for the next renewal will not be accepted without a complete set of documents according to the order.
The order comes after revelations last year that a number of embassies in Thailand, including the UK, USA and Australia, would stop issuing income letters or affidavits, which had been used by expats to confirm their income when applying for a retirement or marriage extension.
Best to consult a local visa agent or go directly to your local Immigration office for an ‘off the record’ chat before you submit your documents.