A recent study by NetCredit has estimated that a person would need, on average, $390,000 USD to retire comfortably in Thailand. The study based the amount on average equivalent quality of life a foreigner would enjoy in their native, home country. Although this is not true for every person, it is a good starting point in which to base your retirement funds.
To apply for a retirement visa in Thailand, the law dictates that applicants should have a savings of 800,000 THB or $25,000 USD in a Thai bank account. Another option is to show funds being deposited monthly into your Thai bank account in the amount of 65,000 THB or $2,000 USD.