diff --git a/popup/popup.html b/popup/popup.html
index 4ebe3fa..fdbd456 100644
--- a/popup/popup.html
+++ b/popup/popup.html
@@ -53,7 +53,7 @@
                 <label for="deltaAppt">Appointment delta (days)</label>
             </div>
             <div class="col">
-                <input type="number" class="form-control" id="deltaAppt" placeholder="days">
+                <input type="number" class="form-control" id="deltaAppt" placeholder="days" min="1" max="365">
             </div>
         </div>
         <div class="row">
@@ -61,7 +61,7 @@
                 <label for="deltaNow">Preparation time (days)</label>
             </div>
             <div class="col">
-                <input type="number" class="form-control" id="deltaNow" placeholder="days">
+                <input type="number" class="form-control" id="deltaNow" placeholder="days" min="1" max="365">
             </div>
         </div>
         <div class="row">