diff --git a/hw/cxl/cxl-mailbox-utils.c b/hw/cxl/cxl-mailbox-utils.c
index 9f794e4655..3a93966e77 100644
--- a/hw/cxl/cxl-mailbox-utils.c
+++ b/hw/cxl/cxl-mailbox-utils.c
@@ -2879,7 +2879,8 @@ static void bg_timercb(void *opaque)
         }
     } else {
         /* estimate only */
-        cci->bg.complete_pct = 100 * now / total_time;
+        cci->bg.complete_pct =
+            100 * (now - cci->bg.starttime) / cci->bg.runtime;
         timer_mod(cci->bg.timer, now + CXL_MBOX_BG_UPDATE_FREQ);
     }