U.S. Office of Personnel Management - Ensuring the Federal Government has an effective civilian workforce

If you lose FEHB coverage other than by cancellation (including cancellation by nonpayment of premiums), you have a 31-day temporary extension of coverage, at no cost, in the same enrollment category held at separation. TCC (temporary continuation of coverage) takes effect on the day that the 31-day temporary extension of coverage ends. Coverage is retroactive to that date if the enrollment processing is completed later.

As previously discussed, depending on the circumstances, a timely election can be made up to 120 days after the qualifying event. If you wait that long to enroll, you are billed for the entire 89-day period of retroactive coverage. In cases where the employing office accepts a belated election, the period of retroactive coverage for which you are billed is even longer.

If you do not pay the bill for the retroactive coverage, the TCC enrollment is canceled retroactively to the beginning date and you are not eligible to reenroll.