diff --git a/config/config.default.php b/config/config.default.php
index 98f41785..041bf6ef 100644
--- a/config/config.default.php
+++ b/config/config.default.php
@@ -207,9 +207,16 @@ return [
     // Setting this to 0 disables the feature
     'signup_advance_hours'    => env('SIGNUP_ADVANCE_HOURS', 0),
 
-    // Allow signup this many minutes after the start of the shift
+    // Allow signup this many minutes after the start of the shift.
+    // If signup_post_fraction is set, first applies that before adding the number of minutes specified by this.
     'signup_post_minutes'     => env('SIGNUP_POST_MINUTES', 0),
 
+    // Allow signup this fraction of the shift length after the start of the shift.
+    // Example: If this is set to 1, signup is allowed until the end of a shift
+    //          If this is set to 0.5, signup is allowd for the first half of a shift
+    // If signup_post_minutes is set, first applies this and then adds the signup_post_minutes on top.
+    'signup_post_fraction'    => env('SIGNUP_POST_FRACTION', 0),
+
     // Number of hours that an angel has to sign out own shifts
     'last_unsubscribe'        => env('LAST_UNSUBSCRIBE', 3),
 
diff --git a/includes/model/Shifts_model.php b/includes/model/Shifts_model.php
index 107430c0..96ec0033 100644
--- a/includes/model/Shifts_model.php
+++ b/includes/model/Shifts_model.php
@@ -358,7 +358,9 @@ function Shift_signup_allowed_angel(
         return new ShiftSignupState(ShiftSignupState::SIGNED_UP, $free_entries);
     }
 
-    if (time() > $shift['start'] + config('signup_post_minutes') * 60) {
+    $shift_post_signup_total_allowed_seconds = (config('signup_post_fraction') * ($shift['end'] - $shift['start'])) + (config('signup_post_minutes') * 60);
+
+    if (time() > $shift['start'] + $shift_post_signup_total_allowed_seconds) {
         // you can only join if the shift is in future
         return new ShiftSignupState(ShiftSignupState::SHIFT_ENDED, $free_entries);
     }