There is a common belief that sunscreen is only good for one season. Some will have expiration dates printed on them. However, most sunscreens do not have expiration dates printed on them. Instead "lot numbers" can be used to determine the date the product was manufactured.

For Coppertone products, the first character of the lot code represents the year of manufacture (7=2007, etc). The second character is a bit more involved. It will tell you the month of manufacture using this code: A=Jan, B=Feb, C=Mar, D=Apr, E=May, but then G=June, H=July, J=Aug, K=Sept, M=Oct, N=Nov, and P=Dec.

Per Scherring-Plough (the mfr of Coppertone) their SPF sunscreens have a shelf life of 3 years from the date of manufacture.

For Banana Boat products, the first 2 digits of the code represent the year it was made (07=2007, etc.) and the next 3 digits represent the day of the year (32=Feb 1st, 365=Dec 31st, etc). They also state a shelf life of 3 years.