Texas Finance Code - FIN § 347.104. Amount of Rate Adjustment

(a) The amount of a rate adjustment is computed by subtracting the index base or, for a change after the initial change, the index value used for the preceding rate adjustment from the index value on the first day of a month that precedes the 50th day before the date on which the adjustment is to take effect.  The amount is applied to the rate applicable to the credit transaction.

(b) The rate in a credit transaction may be adjusted only if the adjustment results in a change of at least one-eighth of one percent a year.