diff --git a/src/models/Store.lua b/src/models/Store.lua
index 9031af0..8ab41ff 100644
--- a/src/models/Store.lua
+++ b/src/models/Store.lua
@@ -73,7 +73,7 @@ function Store:sendMonthCardEmail()
             if ts == 0 then
                 cnt = 1
             else
-                local diff = dayLater(timeNow) - dayLater(ts)
+                local diff = math.floor((dayLater(timeNow) - dayLater(ts))/DAY_SEC)
                 diff = diff < 0 and 0 or diff
                 diff = diff > 31 and 31 or diff
                 cnt = diff
--
libgit2 0.21.2