You may apply for a new ESTA before or after a previous one has expired. There are no restrictions on the number of times you can obtain a new ESTA authorization which is valid for two years from the date of issue. If you wanted to, you even could apply for a new ESTA again the day after obtaining the previous one.
How many times can you apply for an ESTA?
Your ESTA authorization is generally valid for multiple trips over a period of two years (starting the date that you are approved) or until your passport expires, whichever comes first. As long as you received an ESTA authorization to travel, you do not have to reapply during the validity period.
How many ESTA can you have?
There is no limit on the number of times you may enter the U.S. under either ESTA of a visa. However, if reentering the U.S. using ESTA soon after staying for nearly 90 days, you can expect to be questioned in detail by the immigration officer about the purpose of your visit.
Can an ESTA visa be extended?
If your Electronic System for Travel Authorization (ESTA) has expired, you must reapply for a brand new authorization by submitting a new application. Current authorizations can not be extended. ESTA approvals are typically granted for a two-year period or until the applicants passport expires, whichever is sooner.