The corporate loan rate is expected to rise in line with higher funding costs after banks raised fixed-deposit rates.
Some banks can charge corporate customers a higher rate after their financial costs increase, as they lifted fixed-deposit rates across the board, said Predee Daochai, chairman of the Thai Bankers' Association.
This will vary among banks, given different interest structures, financial costs and liquidity, Mr Predee said.
Although banks recently raised fixed-deposit rates by a quarter percentage point, the increased rate is insignificant and won't compel banks to raise prime lending rates, he said.
Prime rates are the minimum lending rate (MLR), minimum overdraft rate and minimum retail rate.
Siam Commercial Bank (SCB) and Kasikornbank (KBank) last week raised their fixed-deposit rates by 25 basis points, following in the footsteps of Government Savings Bank, which partially passed through the central bank's higher rate in December.
On Dec 19, the central bank hiked its one-day repurchase rate by 25 basis points to 1.75% after keeping the rate at 1.5% since 2015. Economists expect one or two increases in the benchmark rate this year.
Bank of Thailand governor Veerathai Santiprabhob said late last year that the policy rate hike would compel banks to lower the discount rate for corporate borrowers. Banks' underpricing of risk in extending loans to corporate firms by offering them a large discount to MLR is an area of concern for the central bank, as big companies have been found to borrow cheaply for riskier investments.
"For prime lending rates, a rate hike at this time could affect borrowers amid economic uncertainties, while the Federal Reserve is likely to increase its policy rate at a slower pace than earlier expected this year," Mr Predee said.
Arak Sutivong, chief financial officer of SCB, said it's normal practice to increase rates in line with risk and return.
KBank president Kattiya Indaravijaya said the bank's interest rates for corporate customers remain unchanged at the moment.
Bangkok Bank (BBL) executive chairman Deja Tulananda said a rate increase is not in the bank's plans at the moment, given the liquidity surplus and unchanged rates for corporate borrowers.
BBL's rate movements will depend on its own internal conditions, he said.
Kasikorn Research Center, a research unit under KBank, expects some commercial banks to begin passing on the central bank's higher rate to fixed deposits, mortgages and auto loans in the first half of 2019.