diff --git a/package-lock.json b/package-lock.json
index 6c2bcbd..d1a0bdb 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -17,10 +17,12 @@
 				"fastify": "^5.6.2",
 				"fastify-axios": "^1.3.0",
 				"fastify-type-provider-zod": "^6.1.0",
+				"luxon": "^3.7.2",
 				"swagger-themes": "^1.4.3",
 				"zod": "^4.1.12"
 			},
 			"devDependencies": {
+				"@types/luxon": "^3.7.1",
 				"@types/node": "^24.10.1",
 				"@types/ws": "^8.18.1",
 				"tsx": "^4.20.6",
@@ -780,6 +782,13 @@
 			"integrity": "sha512-k2ENnmBugE/rzQfEcdWHcCY+/FM3VLzH9cYEsbdsoqrvzAKRhUZeRNhAZvB8OitQJ1TBed3yqWtdjzS6wJKBwg==",
 			"license": "MIT"
 		},
+		"node_modules/@types/luxon": {
+			"version": "3.7.1",
+			"resolved": "https://registry.npmjs.org/@types/luxon/-/luxon-3.7.1.tgz",
+			"integrity": "sha512-H3iskjFIAn5SlJU7OuxUmTEpebK6TKB8rxZShDslBMZJ5u9S//KM1sbdAisiSrqwLQncVjnpi2OK2J51h+4lsg==",
+			"dev": true,
+			"license": "MIT"
+		},
 		"node_modules/@types/node": {
 			"version": "24.10.11",
 			"resolved": "https://registry.npmjs.org/@types/node/-/node-24.10.11.tgz",
@@ -1586,6 +1595,15 @@
 				"node": "20 || >=22"
 			}
 		},
+		"node_modules/luxon": {
+			"version": "3.7.2",
+			"resolved": "https://registry.npmjs.org/luxon/-/luxon-3.7.2.tgz",
+			"integrity": "sha512-vtEhXh/gNjI9Yg1u4jX/0YVPMvxzHuGgCm6tC5kZyb08yjGWGnqAjGJvcXbqQR2P3MyMEFnRbpcdFS6PBcLqew==",
+			"license": "MIT",
+			"engines": {
+				"node": ">=12"
+			}
+		},
 		"node_modules/math-intrinsics": {
 			"version": "1.1.0",
 			"resolved": "https://registry.npmjs.org/math-intrinsics/-/math-intrinsics-1.1.0.tgz",
diff --git a/package.json b/package.json
index bac2030..235a070 100644
--- a/package.json
+++ b/package.json
@@ -22,10 +22,12 @@
 		"fastify": "^5.6.2",
 		"fastify-axios": "^1.3.0",
 		"fastify-type-provider-zod": "^6.1.0",
+		"luxon": "^3.7.2",
 		"swagger-themes": "^1.4.3",
 		"zod": "^4.1.12"
 	},
 	"devDependencies": {
+		"@types/luxon": "^3.7.1",
 		"@types/node": "^24.10.1",
 		"@types/ws": "^8.18.1",
 		"tsx": "^4.20.6",
diff --git a/src/grist/service.ts b/src/grist/service.ts
index 0e24750..3f3d5c1 100644
--- a/src/grist/service.ts
+++ b/src/grist/service.ts
@@ -4,6 +4,7 @@ import {
 	logWarning,
 	type ServiceResult,
 } from "@dpu/shared";
+import { DateTime } from "luxon";
 import { Config } from "../config.js";
 import type { GristClient } from "./client.js";
 
@@ -35,9 +36,13 @@ export class GristService extends BaseService<GristClient> {
 		}
 	}
 
-	private getTodayAsId(date = new Date()) {
-		const start = new Date(date.getFullYear(), 0, 0);
-		const diff = date.getTime() - start.getTime();
+	private getTodayAsId() {
+		const now = DateTime.now().setZone("Europe/Berlin");
+		const start = DateTime.fromObject(
+			{ year: now.year, month: 0, day: 0, hour: 0, minute: 0 },
+			{ zone: "Europe/Berlin" },
+		);
+		const diff = start.diff(now).toMillis();
 		return Math.floor(diff / 86400000);
 	}