diff --git a/plugins/vocabbuilder.koplugin/db.lua b/plugins/vocabbuilder.koplugin/db.lua
index 354db8f72..236505306 100644
--- a/plugins/vocabbuilder.koplugin/db.lua
+++ b/plugins/vocabbuilder.koplugin/db.lua
@@ -227,7 +227,7 @@ function VocabularyBuilder:gotOrForgot(item, isGot)
     elseif target_count == 7 then
         due_time = current_time + 24 * 15 * 3600
     else
-        due_time = current_time + 24 * 30 * 3600
+        due_time = current_time + 24 * 3600 * 30 * 2 ^ (math.min(target_count - 8, 6))
     end
 
     item.last_streak_count = item.streak_count
diff --git a/plugins/vocabbuilder.koplugin/main.lua b/plugins/vocabbuilder.koplugin/main.lua
index 5c5b4a2f6..716a0a5b2 100644
--- a/plugins/vocabbuilder.koplugin/main.lua
+++ b/plugins/vocabbuilder.koplugin/main.lua
@@ -932,13 +932,17 @@ function VocabItemWidget:getTimeSinceDue()
 
     local rounding = elapsed > 0 and math.floor or math.ceil
     if abs < 60 then
-        readable_time = abs .. C_("Time", "s")
+        readable_time = T(C_("Time", "%1s"), abs)
     elseif abs < 3600 then
-        readable_time = string.format("%d"..C_("Time", "m"), rounding(abs/60))
+        readable_time = T(C_("Time", "%1m"), rounding(abs/60))
     elseif abs < 3600 * 24 then
-        readable_time = string.format("%d"..C_("Time", "h"), rounding(abs/3600))
+        readable_time = T(C_("Time", "%1h"), rounding(abs/3600))
+    elseif abs < 3600 * 24 * 30 then
+        readable_time = T(C_("Time", "%1d"), rounding(abs/3600/24))
+    elseif abs < 3600 * 24 * 365 then
+        readable_time = T(C_("Time", "%1 mo."), rounding(abs/3600/24/3)/10)
     else
-        readable_time = string.format("%d"..C_("Time", "d"), rounding(abs/3600/24))
+        readable_time = T(C_("Time", "%1 yr."), rounding(abs/3600/24/36.5)/10)
     end
 
     if elapsed < 0 then