Advance date query

Can you please let me know the command that will enable me to find all the customers WHERE contractEnds in the next 30 days?
Here is my current query:

------------------------------------------------
SELECT BusinessName, ContractStart, ContractEnd
FROM customers_tbl
WHERE ContractEnd <= 30
-------------------------------------------------
About the ContractEnd field: I use MySQL and the field is set as DATE
Year-Month-Day
0000-00-00
I will really appreciate your help.
Thanks

WHERE CURDATE() <= ContractEnd - INTERVAL 30 DAY

date-and-time-functions.html#function_date-add

Fantastic!
Thank you so much.
One final question and I'll be extremely happy if you will be able to answer this question.
"SELECT * FROM customers_tbl WHERE CURDATE() >= ContractEnd - INTERVAL 30 DAY"

The above will let me know customers who have to renew their contract in less than 30 days and it will display all the records below the +30 days
So far very good

I will like to control this by stopping on -30 DAY.
So the records will be +30 and -30
At the moment it shows every single record below the +30 including contracts have ended in 2005

Is this possible?
You will be the best programming helper if you will be able to give me the answer.
Looking forward for the answer.
THANKS THANKS THANKS!!!

SELECT * FROM customers_tbl WHERE CURDATE() >= ContractEnd - INTERVAL 30 DAY AND CURDATE() <= ContractEnd + INTERVAL 30 DAY

What a man
You are the best

Thank you very much