diff --git a/src/components/Proposal/ProposalDateItem.vue b/src/components/Proposal/ProposalDateItem.vue
index 1a25165d82..7d28156a16 100644
--- a/src/components/Proposal/ProposalDateItem.vue
+++ b/src/components/Proposal/ProposalDateItem.vue
@@ -28,6 +28,7 @@ import moment from '@nextcloud/moment'
 // icons
 import ItemIcon from 'vue-material-design-icons/Calendar'
 import DestroyIcon from 'vue-material-design-icons/Close'
+import { getTimezoneOffset } from '@/services/timezoneOffsetService'
 
 export default {
 	name: 'ProposalDateItem',
@@ -57,15 +58,7 @@ export default {
 				return ''
 			}
 			// Get the timezone offset in minutes
-			let timezoneOffset = 0
-			try {
-				const now = new Date()
-				const utcDate = new Date(now.toLocaleString('en-US', { timeZone: 'UTC' }))
-				const targetDate = new Date(now.toLocaleString('en-US', { timeZone: this.timezoneId }))
-				timezoneOffset = ((utcDate.getTime() - targetDate.getTime()) / (1000 * 60)) * -1
-			} catch (e) {
-				timezoneOffset = 0
-			}
+			const timezoneOffset = getTimezoneOffset(this.proposalDate.date, this.timezoneId)
 			const m = moment(this.proposalDate.date).utcOffset(timezoneOffset)
 			// Examples: "Mon, Jul 8, 2:30 PM" (en), "Mon, 8 Jul, 14:30" (en-GB), "Mo, 8. Jul, 14:30" (de)
 			return m.format('dddd, MMMM D, LT')
diff --git a/src/components/Proposal/ProposalResponseMatrix.vue b/src/components/Proposal/ProposalResponseMatrix.vue
index 3e769a0425..fff643fb4f 100644
--- a/src/components/Proposal/ProposalResponseMatrix.vue
+++ b/src/components/Proposal/ProposalResponseMatrix.vue
@@ -137,6 +137,7 @@ import NcAvatar from '@nextcloud/vue/components/NcAvatar'
 import NcButton from '@nextcloud/vue/components/NcButton'
 import NcCheckboxRadioSwitch from '@nextcloud/vue/components/NcCheckboxRadioSwitch'
 import { Proposal, ProposalResponse } from '@/models/proposals/proposals'
+import { getTimezoneOffset } from '@/services/timezoneOffsetService'
 import { ProposalDateVote } from '@/types/proposals/proposalEnums'
 
 export default {
@@ -182,7 +183,6 @@ export default {
 	data() {
 		return {
 			ProposalDateVote,
-			timezoneOffset: 0,
 		}
 	},
 
@@ -201,17 +201,21 @@ export default {
 			const groups = {}
 			dates.forEach((d) => {
 				// Apply timezone offset for grouping by day
-				const key = d.date ? moment(d.date).utcOffset(this.timezoneOffset).format('yyyy-MM-dd') : 'invalid'
+				const offset = getTimezoneOffset(d.date.toISOString(), this.timezoneId)
+				const key = moment(d.date).utcOffset(offset).format('YYYY-MM-DD')
 				if (!groups[key]) {
 					groups[key] = []
 				}
 				groups[key].push(d)
 			})
-			return Object.entries(groups).map(([key, grp]: [string, ProposalDate[]]) => ({
-				key,
-				label: moment(grp[0].date).utcOffset(this.timezoneOffset).format('dddd, MMMM Do'),
-				dates: grp,
-			}))
+			return Object.entries(groups).map(([key, grp]: [string, ProposalDate[]]) => {
+				const offset = getTimezoneOffset(grp[0].date.toISOString(), this.timezoneId)
+				return {
+					key,
+					label: moment(grp[0].date).utcOffset(offset).format('dddd, MMMM Do'),
+					dates: grp,
+				}
+			})
 		},
 
 		columnCount() {
@@ -222,39 +226,13 @@ export default {
 
 	},
 
-	watch: {
-		timezoneId(newZone) {
-			if (newZone) {
-				this.timezoneOffset = this.calculateTimezoneOffset(newZone)
-			}
-		},
-	},
-
-	created() {
-		if (this.timezoneId) {
-			this.timezoneOffset = this.calculateTimezoneOffset(this.timezoneId)
-		}
-	},
-
 	methods: {
 		t,
 
-		calculateTimezoneOffset(timezoneId) {
-			// Get the timezone offset in minutes
-			try {
-				const now = new Date()
-				const utcDate = new Date(now.toLocaleString('en-US', { timeZone: 'UTC' }))
-				const targetDate = new Date(now.toLocaleString('en-US', { timeZone: timezoneId }))
-				return ((utcDate.getTime() - targetDate.getTime()) / (1000 * 60)) * -1
-			} catch (e) {
-				// Fallback to UTC if timezone is invalid
-				return 0
-			}
-		},
-
 		dateTimeSpan(date) {
-			const startDate = moment(date).utcOffset(this.timezoneOffset)
-			const endDate = moment(date).utcOffset(this.timezoneOffset).add(this.proposal.duration, 'minutes')
+			const offset = getTimezoneOffset(date.toISOString(), this.timezoneId)
+			const startDate = moment(date).utcOffset(offset)
+			const endDate = moment(date).utcOffset(offset).add(this.proposal.duration, 'minutes')
 
 			const startTime = startDate.format('LT')
 			const endTime = endDate.format('LT')
@@ -277,7 +255,8 @@ export default {
 				return ''
 			}
 			// Apply timezone offset and format very compact: "7/8 2PM"
-			const adjustedDate = moment(date).utcOffset(this.timezoneOffset)
+			const offset = getTimezoneOffset(date.toISOString(), this.timezoneId)
+			const adjustedDate = moment(date).utcOffset(offset)
 			return adjustedDate.format('M/D LT').replace(':00', '').replace(' ', ' ')
 		},
 
diff --git a/src/services/timezoneOffsetService.js b/src/services/timezoneOffsetService.js
new file mode 100644
index 0000000000..44f8d1e64a
--- /dev/null
+++ b/src/services/timezoneOffsetService.js
@@ -0,0 +1,52 @@
+/**
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+const dtfCache = new Map()
+
+export function getTimezoneOffset(proposalDate, timezoneId) {
+	try {
+		const date = new Date(proposalDate)
+		if (isNaN(date)) {
+			return null
+		}
+
+		let dtf = dtfCache.get(timezoneId)
+		if (!dtf) {
+			dtf = new Intl.DateTimeFormat('en-US', {
+				timeZone: timezoneId,
+				hour12: false,
+				year: 'numeric',
+				month: '2-digit',
+				day: '2-digit',
+				hour: '2-digit',
+				minute: '2-digit',
+				second: '2-digit',
+			})
+			dtfCache.set(timezoneId, dtf)
+		}
+
+		const parts = dtf.formatToParts(date)
+		const values = {}
+
+		for (const { type, value } of parts) {
+			if (type !== 'literal') {
+				values[type] = value
+			}
+		}
+
+		const asUTC = Date.UTC(
+			Number(values.year),
+			Number(values.month) - 1,
+			Number(values.day),
+			Number(values.hour),
+			Number(values.minute),
+			Number(values.second),
+		)
+
+		return Math.floor((asUTC - date.getTime()) / 60000)
+	} catch {
+		return null
+	}
+}