After you have consulted your doctor(s) and determined that you may be unable to work for a period of 12 months or more, you should file for your benefits immediately. You could risk losing the benefits that you are legally entitled to if you wait longer than necessary to apply.
If you are found eligible to receive Disability Insurance Benefits, you can only recover retroactive benefits for the 12 months prior to submitting your application. If you wait more than a year from the day you stop working to submit your application, you risk losing more benefits with each passing day.
Depending on how much you have paid into Social Security over your working years, this could mean the loss of thousands of dollars per month. If you are found eligible for Supplemental Security Income, you are only eligible to receive benefits based upon the date of your application.
It is extremely important that you apply for your benefits as soon as possible. Every month that you do not apply, you may be losing much needed back-benefits.