diff --git a/ThemeParkClicker/Ui.cs b/ThemeParkClicker/Ui.cs
index 7afb5a6..a2b5691 100644
--- a/ThemeParkClicker/Ui.cs
+++ b/ThemeParkClicker/Ui.cs
@@ -138,8 +138,9 @@ namespace ThemeParkClicker {
                     },
                     OnAreaUpdated = e => {
                         // only update the price when the area updates, since it won't change while we're in the buy ui
-                        var markup = GameImpl.Instance.Map.GetAttractionAmount(attraction.Value) * 0.05F;
-                        price = (attraction.Value.InitialPrice * (1 + markup)).Ceil();
+                        var amount = GameImpl.Instance.Map.GetAttractionAmount(attraction.Value);
+                        // yay compound interest
+                        price = (attraction.Value.InitialPrice * (float) Math.Pow(1 + 0.1F, amount)).Ceil();
                     }
                 });
                 button.OnUpdated += (e, time) => {