Chai means life, and 18 is the number. Honest, traditional, and always the right answer.
In Hebrew, letters double as numbers, and the letters of the word chai, life, add up to 18. So Jewish gift-givers give in multiples of 18: $36, $54, $72, $180 and up. It is a way of literally wishing someone life and blessing with the amount itself, and it is one of the most beloved traditions in Jewish gift-giving.
It is honest and it is practical. The bar or bat mitzvah kid, the wedding couple, they know what they want better than you do, and money in a heartfelt card goes exactly where it is needed. There is nothing to return, nothing to store, nothing that misses. Scale the number to your relationship and you are done.
The card is where the real gift lives. A few genuine words about what you wish for them, wrapped around a number that means life, is quietly one of the best gifts at any Jewish celebration. The tradition does the rest.
The bar or bat mitzvah, the wedding couple, or any milestone where you want to give something honest and meaningful. Every bubbe already knows this is the answer.
Your own checkbook or a nice card. The tradition is the gift, pair it with a heartfelt handwritten note.