diff --git a/package-lock.json b/package-lock.json
index aa6b722..e627b1d 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -30,6 +30,7 @@
         "daisyui": "^2.20.0",
         "date-fns": "^2.29.1",
         "froebel": "^0.18.0",
+        "ibantools": "^4.1.6",
         "myzod": "^1.8.7",
         "nanoid": "^4.0.0",
         "node-iso11649": "^2.1.2",
@@ -4249,6 +4250,12 @@
         "node": ">=10.17.0"
       }
     },
+    "node_modules/ibantools": {
+      "version": "4.1.6",
+      "resolved": "https://registry.npmjs.org/ibantools/-/ibantools-4.1.6.tgz",
+      "integrity": "sha512-BpIqMJj6tgFbx1YmH7tjstiqf8VgLkGL2d3K7XSOuGxbdy6gv6ovKjC/Yqgrh3OEeqeSzx8fVu5P96Q1bWg2bg==",
+      "dev": true
+    },
     "node_modules/indent-string": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/indent-string/-/indent-string-4.0.0.tgz",
@@ -11180,6 +11187,12 @@
       "resolved": "https://registry.npmjs.org/human-signals/-/human-signals-2.1.0.tgz",
       "integrity": "sha512-B4FFZ6q/T2jhhksgkbEW3HBvWIfDW85snkQgawt07S7J5QXTk6BkNV+0yAeZrM5QpMAdYlocGoljn0sJ/WQkFw=="
     },
+    "ibantools": {
+      "version": "4.1.6",
+      "resolved": "https://registry.npmjs.org/ibantools/-/ibantools-4.1.6.tgz",
+      "integrity": "sha512-BpIqMJj6tgFbx1YmH7tjstiqf8VgLkGL2d3K7XSOuGxbdy6gv6ovKjC/Yqgrh3OEeqeSzx8fVu5P96Q1bWg2bg==",
+      "dev": true
+    },
     "indent-string": {
       "version": "4.0.0",
       "resolved": "https://registry.npmjs.org/indent-string/-/indent-string-4.0.0.tgz",
diff --git a/package.json b/package.json
index 0c901c1..a799ed2 100644
--- a/package.json
+++ b/package.json
@@ -32,6 +32,7 @@
     "daisyui": "^2.20.0",
     "date-fns": "^2.29.1",
     "froebel": "^0.18.0",
+    "ibantools": "^4.1.6",
     "myzod": "^1.8.7",
     "nanoid": "^4.0.0",
     "node-iso11649": "^2.1.2",
diff --git a/src/components/Form.tsx b/src/components/Form.tsx
index c90eed2..23fc663 100644
--- a/src/components/Form.tsx
+++ b/src/components/Form.tsx
@@ -28,6 +28,7 @@ export const TextInput: Component<
     suffix?: string | JSX.Element;
     size?: string;
     vertical?: boolean;
+    invalidate?: (v: any) => string | boolean;
   } & JSX.InputHTMLAttributes<HTMLInputElement>
 > = (p) => {
   p = mergeProps(
@@ -48,6 +49,7 @@ export const TextInput: Component<
     "suffix",
     "vertical",
     "labelMinWidth",
+    "invalidate",
   ]);
   const sizes: Record<string, string> = {
     xs: "input-xs",
@@ -55,7 +57,10 @@ export const TextInput: Component<
     lg: "input-lg",
   };
 
-  const [validate, vState] = validateInput({ value: () => rest.value });
+  const [validate, vState] = validateInput({
+    invalidate: props.invalidate,
+    value: () => rest.value,
+  });
 
   return (
     <div class="shrink form-control">
diff --git a/src/components/Settings/Overlay.tsx b/src/components/Settings/Overlay.tsx
index 1a7704d..b5c1cae 100644
--- a/src/components/Settings/Overlay.tsx
+++ b/src/components/Settings/Overlay.tsx
@@ -17,6 +17,7 @@ import z from "myzod";
 import Big from "big.js";
 import { generate } from "node-iso11649";
 import { customAlphabet } from "nanoid";
+import { isValidIBAN } from "ibantools";
 
 import createAccordion from "../Accordion";
 import {
@@ -534,6 +535,17 @@ const SettingsOverlay: Component = () => {
                       label="Iban"
                       maxLength={50}
                       value={localState.iban}
+                      invalidate={(v) => {
+                        // If the value is empty, the HTML5 "required" attribute will do its own validation, we can skip the IBAN check
+                        if (v === "") {
+                          return false;
+                        }
+
+                        return (
+                          !isValidIBAN(v.replaceAll(" ", "")) &&
+                          "Diese IBAN ist womöglich ungültig."
+                        );
+                      }}
                       onInput={(evt) =>
                         setLocalState("iban", evt.currentTarget.value)
                       }
diff --git a/src/hooks/validation.tsx b/src/hooks/validation.tsx
index 3446fd8..5a8c6c8 100644
--- a/src/hooks/validation.tsx
+++ b/src/hooks/validation.tsx
@@ -40,9 +40,11 @@ const EMPTY_OBJECT = {};
 
 export const validateInput = function ({
   value: getValue,
+  invalidate: invalidate,
   listen,
 }: {
   value?: () => any;
+  invalidate?: (v: any) => string | boolean;
   listen?: {
     input?: boolean;
     blur?: boolean;
@@ -75,6 +77,19 @@ export const validateInput = function ({
       // Update state on badInput (value stays unchanged on badInput), but only update the state once
       validity_.badInput != lastBadInput
     ) {
+      if (invalidate) {
+        const invalidateResult = invalidate(nextValue);
+        if (invalidateResult) {
+          el.setCustomValidity(
+            invalidateResult === true
+              ? "Input value is invalid."
+              : invalidateResult
+          );
+        } else {
+          el.setCustomValidity("");
+        }
+      }
+
       name = name || el.name || el.id;
       setValidity(validity_);
       lastBadInput = validity_.badInput;