‘The word for ‘life’ in Hebrew is ‘chai.’ The two Hebrew letters that make up the word ‘chai’ are chet and yud. In Gematria (the numerical value of Hebrew letters), chet is equivalent to 8 and yud is equivalent to 10. So ‘chai’, chet and yud together, equals 18. Giving money in multiples of $18 is symbolic of giving ‘chai’ or life. Many people give money in multiples of $18 as presents to someone celebrating a birth, a bar or bat mitzvah or a wedding.’
