To motivate private investment in electricity generated from renewable energy in Thailand, an adder program has been firstly subsidized to the wholesale electricity sold to the national grid with a cap on retail electricity price. Since, with the adder program, electricity quantity supplied to the grid was found under expectation, FIT measure has been substituted in some generation technologies with some questions on their proper wholesale price that affects the electricity retail price and the country burden. This study proposes FIT’s in 4 technologies i.e. solar photovoltaics (PV), biomass, wind farm, and small hydro power plant in 2012, by using a financial analysis based on capital and operating data from sites survey and reference data. At least 3 active sites of each technology were surveyed for each technology. With learning experienced in the country and worldwide, expected FITs in 2020 and 2030 were forecasted. As a results, in 2012, proposed solar PV FIT was 6.12-7.12 Baht/kWh as the highest one, and biomass FIT was 3.10–3.30 Baht/kWh as the lowest one. Expected FITs for small hydro and wind farm in 2012 were 4.50–7.00 Baht/kWh and 6.02 Baht/kWh, respectively. The future FITs for solar PV and wind turbine were forecasted to decrease due to expecting decreasing in their capital cost. In the other hands, FITs for small hydro and biomass power plants were expecting to increased, accordingly to increasing in capital cost of these power plants and fuel price. Average FITs that grid has to subsidize to renewable electricity producer are estimated to be fixed annually in long-term contracts, according to each technology’s quantity. These predictions were based on the quantities of renewable electricity generation as expected by Alternative Energy Development Plan 2012–2021 and prioritized according to PDP2010 during 2010-2030. A long term comparative assessment presents that the FIT policy under PDP2010 could induce less subsidizing burden and finally induces less Ft than the Adder policy.