If you make a withdrawal from a TFSA, the amount of the withdrawal is added to your available contribution room the next calendar year on January 1st.

For example, say you contributed the maximum amount to your TFSA every year after you turned 18 until 2018. Then in March 2018, you decided to withdraw $10,000. The normal annual contribution maximum would have been $6,000 in 2019, but because you withdrew funds in 2018 your actual contribution room for 2019 would be $16,000 ($6,000 + $10,000)!