Loss from breaking a certificate of deposit isn't calculated using a single, general percentage.
Steps
You need to know the purchase date, the holding period, the issue's redemption schedule, and the returns you've already received.
Ask the bank for the net redemption value today, then compare it to the principal and the returns you would have received had you continued holding the certificate.
This is more accurate than trying to estimate the loss based solely on the certificate's announcement.
The figures, fees and limits in this answer vary by bank and change over time — confirm them with your bank or the official source before acting.