diff --git a/app/src/main/java/io/heckel/ntfy/db/Repository.kt b/app/src/main/java/io/heckel/ntfy/db/Repository.kt
index 43c8c8581..fa12726c6 100644
--- a/app/src/main/java/io/heckel/ntfy/db/Repository.kt
+++ b/app/src/main/java/io/heckel/ntfy/db/Repository.kt
@@ -360,6 +360,22 @@ class Repository(private val sharedPrefs: SharedPreferences, database: Database)
         return sharedPrefs.getString(SHARED_PREFS_CONNECTION_PROTOCOL, null) ?: CONNECTION_PROTOCOL_JSONHTTP
     }
 
+    fun setDateTimeFormat(dateTimeFormat: String) {
+        if (dateTimeFormat == DATETIME_FORMAT_LOCALE) {
+            sharedPrefs.edit {
+                remove(SHARED_PREFS_DATETIME_FORMAT)
+            }
+        } else {
+            sharedPrefs.edit {
+                putString(SHARED_PREFS_DATETIME_FORMAT, dateTimeFormat)
+            }
+        }
+    }
+
+    fun getDateTimeFormat(): String {
+        return sharedPrefs.getString(SHARED_PREFS_DATETIME_FORMAT, DATETIME_FORMAT_LOCALE) ?: DATETIME_FORMAT_LOCALE
+    }
+
     fun getBroadcastEnabled(): Boolean {
         return sharedPrefs.getBoolean(SHARED_PREFS_BROADCAST_ENABLED, true) // Enabled by default
     }
@@ -611,6 +627,7 @@ class Repository(private val sharedPrefs: SharedPreferences, database: Database)
         const val SHARED_PREFS_AUTO_DOWNLOAD_MAX_SIZE = "AutoDownload"
         const val SHARED_PREFS_AUTO_DELETE_SECONDS = "AutoDelete"
         const val SHARED_PREFS_CONNECTION_PROTOCOL = "ConnectionProtocol"
+        const val SHARED_PREFS_DATETIME_FORMAT = "DateTimeFormat"
         const val SHARED_PREFS_DARK_MODE = "DarkMode"
         const val SHARED_PREFS_DYNAMIC_COLORS = "DynamicColors"
         const val SHARED_PREFS_BROADCAST_ENABLED = "BroadcastEnabled"
@@ -655,6 +672,9 @@ class Repository(private val sharedPrefs: SharedPreferences, database: Database)
         const val CONNECTION_PROTOCOL_JSONHTTP = "jsonhttp"
         const val CONNECTION_PROTOCOL_WS = "ws"
 
+        const val DATETIME_FORMAT_LOCALE = "locale"
+        const val DATETIME_FORMAT_ISO8601 = "iso8601"
+
         const val BATTERY_OPTIMIZATIONS_REMIND_TIME_ALWAYS = 1L
         const val BATTERY_OPTIMIZATIONS_REMIND_TIME_NEVER = Long.MAX_VALUE
 
diff --git a/app/src/main/java/io/heckel/ntfy/ui/DetailActivity.kt b/app/src/main/java/io/heckel/ntfy/ui/DetailActivity.kt
index b2554a875..6fa17dda5 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/DetailActivity.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/DetailActivity.kt
@@ -783,7 +783,7 @@ class DetailActivity : AppCompatActivity(), NotificationFragment.NotificationSet
                     0L -> Toast.makeText(this@DetailActivity, getString(R.string.notification_dialog_enabled_toast_message), Toast.LENGTH_LONG).show()
                     1L -> Toast.makeText(this@DetailActivity, getString(R.string.notification_dialog_muted_forever_toast_message), Toast.LENGTH_LONG).show()
                     else -> {
-                        val formattedDate = formatDateShort(mutedUntilTimestamp)
+                        val formattedDate = formatDateShort(this@DetailActivity, mutedUntilTimestamp)
                         Toast.makeText(this@DetailActivity, getString(R.string.notification_dialog_muted_until_toast_message, formattedDate), Toast.LENGTH_LONG).show()
                     }
                 }
@@ -843,7 +843,7 @@ class DetailActivity : AppCompatActivity(), NotificationFragment.NotificationSet
                 notificationsDisabledForeverItem?.isVisible = subscriptionMutedUntil == 1L
                 notificationsDisabledUntilItem?.isVisible = subscriptionMutedUntil > 1L
                 if (subscriptionMutedUntil > 1L) {
-                    val formattedDate = formatDateShort(subscriptionMutedUntil)
+            val formattedDate = formatDateShort(this, subscriptionMutedUntil)
                     notificationsDisabledUntilItem?.title = getString(R.string.detail_menu_notifications_disabled_until, formattedDate)
                 }
             }
@@ -975,7 +975,7 @@ class DetailActivity : AppCompatActivity(), NotificationFragment.NotificationSet
             val content = adapter.selected.joinToString("\n\n") { notificationId ->
                 val notification = repository.getNotification(notificationId)
                 notification?.let {
-                    decodeMessage(it) + "\n" + Date(it.timestamp * 1000).toString()
+                    decodeMessage(it) + "\n" + formatDateShort(this@DetailActivity, it.timestamp)
                 }.orEmpty()
             }
             runOnUiThread {
diff --git a/app/src/main/java/io/heckel/ntfy/ui/DetailAdapter.kt b/app/src/main/java/io/heckel/ntfy/ui/DetailAdapter.kt
index dd2187f87..9c974d0aa 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/DetailAdapter.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/DetailAdapter.kt
@@ -115,7 +115,7 @@ class DetailAdapter(private val activity: Activity, private val lifecycleScope:
             val unmatchedTags = unmatchedTags(splitTags(notification.tags))
             val message = maybeAppendActionErrors(formatMessage(notification), notification)
 
-            dateView.text = formatDateShort(notification.timestamp)
+            dateView.text = formatDateShort(context, notification.timestamp)
             if (notification.isMarkdown()) {
                 messageView.autoLinkMask = 0
                 markwon.setMarkdown(messageView, message.toString())
@@ -353,7 +353,7 @@ class DetailAdapter(private val activity: Activity, private val lifecycleScope:
                 if (expired) {
                     infos.add(context.getString(R.string.detail_item_download_info_not_downloaded_expired))
                 } else if (expires) {
-                    infos.add(context.getString(R.string.detail_item_download_info_not_downloaded_expires_x, formatDateShort(attachment.expires)))
+                infos.add(context.getString(R.string.detail_item_download_info_not_downloaded_expires_x, formatDateShort(context, attachment.expires)))
                 } else {
                     infos.add(context.getString(R.string.detail_item_download_info_not_downloaded))
                 }
@@ -363,7 +363,7 @@ class DetailAdapter(private val activity: Activity, private val lifecycleScope:
                 if (expired) {
                     infos.add(context.getString(R.string.detail_item_download_info_deleted_expired))
                 } else if (expires) {
-                    infos.add(context.getString(R.string.detail_item_download_info_deleted_expires_x, formatDateShort(attachment.expires)))
+                infos.add(context.getString(R.string.detail_item_download_info_deleted_expires_x, formatDateShort(context, attachment.expires)))
                 } else {
                     infos.add(context.getString(R.string.detail_item_download_info_deleted))
                 }
@@ -371,7 +371,7 @@ class DetailAdapter(private val activity: Activity, private val lifecycleScope:
                 if (expired) {
                     infos.add(context.getString(R.string.detail_item_download_info_download_failed_expired))
                 } else if (expires) {
-                    infos.add(context.getString(R.string.detail_item_download_info_download_failed_expires_x, formatDateShort(attachment.expires)))
+                infos.add(context.getString(R.string.detail_item_download_info_download_failed_expires_x, formatDateShort(context, attachment.expires)))
                 } else {
                     infos.add(context.getString(R.string.detail_item_download_info_download_failed))
                 }
diff --git a/app/src/main/java/io/heckel/ntfy/ui/DetailSettingsActivity.kt b/app/src/main/java/io/heckel/ntfy/ui/DetailSettingsActivity.kt
index f0293c79c..fa343eb69 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/DetailSettingsActivity.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/DetailSettingsActivity.kt
@@ -253,7 +253,7 @@ class DetailSettingsActivity : AppCompatActivity() {
                     Repository.MUTED_UNTIL_SHOW_ALL -> getString(R.string.settings_notifications_muted_until_show_all)
                     Repository.MUTED_UNTIL_FOREVER -> getString(R.string.settings_notifications_muted_until_forever)
                     else -> {
-                        val formattedDate = formatDateShort(mutedUntilValue)
+                        val formattedDate = formatDateShort(requireContext(), mutedUntilValue)
                         getString(R.string.settings_notifications_muted_until_x, formattedDate)
                     }
                 }
diff --git a/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt b/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
index 251a4ba0e..166114ac0 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/MainActivity.kt
@@ -552,7 +552,7 @@ class MainActivity : AppCompatActivity(), AddFragment.SubscribeListener, Notific
             notificationsDisabledForeverItem?.isVisible = mutedUntilSeconds == 1L
             notificationsDisabledUntilItem?.isVisible = mutedUntilSeconds > 1L
             if (mutedUntilSeconds > 1L) {
-                val formattedDate = formatDateShort(mutedUntilSeconds)
+                    val formattedDate = formatDateShort(this@MainActivity, mutedUntilSeconds)
                 notificationsDisabledUntilItem?.title = getString(R.string.main_menu_notifications_disabled_until, formattedDate)
             }
         }
@@ -645,7 +645,7 @@ class MainActivity : AppCompatActivity(), AddFragment.SubscribeListener, Notific
                 0L -> Toast.makeText(this@MainActivity, getString(R.string.notification_dialog_enabled_toast_message), Toast.LENGTH_LONG).show()
                 1L -> Toast.makeText(this@MainActivity, getString(R.string.notification_dialog_muted_forever_toast_message), Toast.LENGTH_LONG).show()
                 else -> {
-                    val formattedDate = formatDateShort(mutedUntilTimestamp)
+            val formattedDate = formatDateShort(this, mutedUntilTimestamp)
                     Toast.makeText(this@MainActivity, getString(R.string.notification_dialog_muted_until_toast_message, formattedDate), Toast.LENGTH_LONG).show()
                 }
             }
diff --git a/app/src/main/java/io/heckel/ntfy/ui/MainAdapter.kt b/app/src/main/java/io/heckel/ntfy/ui/MainAdapter.kt
index d10a0ce67..780978a13 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/MainAdapter.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/MainAdapter.kt
@@ -17,9 +17,9 @@ import io.heckel.ntfy.db.ConnectionState
 import io.heckel.ntfy.db.Repository
 import io.heckel.ntfy.db.Subscription
 import io.heckel.ntfy.util.displayName
+import io.heckel.ntfy.util.formatDate
+import io.heckel.ntfy.util.formatTime
 import io.heckel.ntfy.util.readBitmapFromUriOrNull
-import java.text.DateFormat
-import java.util.*
 
 class MainAdapter(
     private val repository: Repository,
@@ -95,14 +95,13 @@ class MainAdapter(
             if (subscription.instant && subscription.connectionDetails.state == ConnectionState.CONNECTING) {
                 statusMessage += ", " + context.getString(R.string.main_item_status_reconnecting)
             }
-            val date = Date(subscription.lastActive * 1000)
-            val dateStr = DateFormat.getDateInstance(DateFormat.SHORT).format(date)
+            val dateStr = formatDate(context, subscription.lastActive)
             val moreThanOneDay = System.currentTimeMillis()/1000 - subscription.lastActive > 24 * 60 * 60
-            val sameDay = dateStr == DateFormat.getDateInstance(DateFormat.SHORT).format(Date()) // Omg this is horrible
+            val sameDay = dateStr == formatDate(context, System.currentTimeMillis() / 1000)
             val dateText = if (subscription.lastActive == 0L) {
                 ""
             } else if (sameDay) {
-                DateFormat.getTimeInstance(DateFormat.SHORT).format(date)
+                formatTime(context, subscription.lastActive)
             } else if (!moreThanOneDay) {
                 context.getString(R.string.main_item_date_yesterday)
             } else {
diff --git a/app/src/main/java/io/heckel/ntfy/ui/SettingsActivity.kt b/app/src/main/java/io/heckel/ntfy/ui/SettingsActivity.kt
index 8ebf2f874..d5de8e322 100644
--- a/app/src/main/java/io/heckel/ntfy/ui/SettingsActivity.kt
+++ b/app/src/main/java/io/heckel/ntfy/ui/SettingsActivity.kt
@@ -209,7 +209,7 @@ class SettingsActivity : AppCompatActivity(), PreferenceFragmentCompat.OnPrefere
                     Repository.MUTED_UNTIL_SHOW_ALL -> getString(R.string.settings_notifications_muted_until_show_all)
                     Repository.MUTED_UNTIL_FOREVER -> getString(R.string.settings_notifications_muted_until_forever)
                     else -> {
-                        val formattedDate = formatDateShort(mutedUntilValue)
+                        val formattedDate = formatDateShort(requireContext(), mutedUntilValue)
                         getString(R.string.settings_notifications_muted_until_x, formattedDate)
                     }
                 }
@@ -351,6 +351,26 @@ class SettingsActivity : AppCompatActivity(), PreferenceFragmentCompat.OnPrefere
                 }
             }
 
+            val dateTimeFormatPrefId = context?.getString(R.string.settings_general_datetime_format_key) ?: return
+            val dateTimeFormat: ListPreference? = findPreference(dateTimeFormatPrefId)
+            dateTimeFormat?.value = repository.getDateTimeFormat()
+            dateTimeFormat?.preferenceDataStore = object : PreferenceDataStore() {
+                override fun putString(key: String?, value: String?) {
+                    val dateTimeFormatValue = value ?: repository.getDateTimeFormat()
+                    repository.setDateTimeFormat(dateTimeFormatValue)
+                }
+
+                override fun getString(key: String?, defValue: String?): String {
+                    return repository.getDateTimeFormat()
+                }
+            }
+            dateTimeFormat?.summaryProvider = Preference.SummaryProvider<ListPreference> { pref ->
+                when (pref.value) {
+                    Repository.DATETIME_FORMAT_ISO8601 -> getString(R.string.settings_general_datetime_format_summary_iso8601)
+                    else -> getString(R.string.settings_general_datetime_format_summary_locale)
+                }
+            }
+
             // Language
             val languagePrefId = context?.getString(R.string.settings_general_language_key) ?: return
             val language: ListPreference? = findPreference(languagePrefId)
diff --git a/app/src/main/java/io/heckel/ntfy/util/Util.kt b/app/src/main/java/io/heckel/ntfy/util/Util.kt
index e472fcefc..9e4630b68 100644
--- a/app/src/main/java/io/heckel/ntfy/util/Util.kt
+++ b/app/src/main/java/io/heckel/ntfy/util/Util.kt
@@ -47,8 +47,11 @@ import java.io.IOException
 import java.security.MessageDigest
 import java.security.SecureRandom
 import java.text.DateFormat
+import java.text.SimpleDateFormat
 import java.text.StringCharacterIterator
 import java.util.Date
+import java.util.Locale
+import java.util.TimeZone
 import kotlin.math.abs
 import kotlin.math.absoluteValue
 import androidx.core.net.toUri
@@ -130,8 +133,41 @@ fun normalizeBaseUrl(url: String): String {
 }
 
 fun formatDateShort(timestampSecs: Long): String {
-    val date = Date(timestampSecs*1000)
-    return DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT).format(date)
+    return formatDateTime(Date(timestampSecs * 1000), Repository.DATETIME_FORMAT_LOCALE)
+}
+
+fun formatDateShort(context: Context, timestampSecs: Long): String {
+    val repository = Repository.getInstance(context)
+    return formatDateTime(Date(timestampSecs * 1000), repository.getDateTimeFormat())
+}
+
+fun formatDate(context: Context, timestampSecs: Long): String {
+    val repository = Repository.getInstance(context)
+    val date = Date(timestampSecs * 1000)
+    return if (repository.getDateTimeFormat() == Repository.DATETIME_FORMAT_ISO8601) {
+        SimpleDateFormat("yyyy-MM-dd", Locale.US).format(date)
+    } else {
+        DateFormat.getDateInstance(DateFormat.SHORT).format(date)
+    }
+}
+
+fun formatTime(context: Context, timestampSecs: Long): String {
+    val repository = Repository.getInstance(context)
+    val date = Date(timestampSecs * 1000)
+    return if (repository.getDateTimeFormat() == Repository.DATETIME_FORMAT_ISO8601) {
+        SimpleDateFormat("HH:mm", Locale.US).format(date)
+    } else {
+        DateFormat.getTimeInstance(DateFormat.SHORT).format(date)
+    }
+}
+
+private fun formatDateTime(date: Date, dateTimeFormat: String): String {
+    return if (dateTimeFormat == Repository.DATETIME_FORMAT_ISO8601) {
+        SimpleDateFormat("yyyy-MM-dd HH:mm", Locale.US)
+            .format(date)
+    } else {
+        DateFormat.getDateTimeInstance(DateFormat.SHORT, DateFormat.SHORT).format(date)
+    }
 }
 
 fun toPriority(priority: Int?): Int {
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 2ac24ce1c..74e74fda2 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -387,6 +387,11 @@
     <string name="settings_general_dark_mode_entry_system">Use system default</string>
     <string name="settings_general_dark_mode_entry_light">Light mode</string>
     <string name="settings_general_dark_mode_entry_dark">Dark mode</string>
+    <string name="settings_general_datetime_format_title">Date/time format</string>
+    <string name="settings_general_datetime_format_summary_locale">Using locale default date/time format</string>
+    <string name="settings_general_datetime_format_summary_iso8601">Using ISO 8601 date/time format</string>
+    <string name="settings_general_datetime_format_entry_locale">Locale default</string>
+    <string name="settings_general_datetime_format_entry_iso8601">ISO 8601</string>
     <string name="settings_general_language_title">Language</string>
     <string name="settings_general_language_summary_system">Using system default</string>
     <string name="settings_general_language_system_default">System default</string>
diff --git a/app/src/main/res/values/values.xml b/app/src/main/res/values/values.xml
index 0b45baf59..bc5ecb775 100644
--- a/app/src/main/res/values/values.xml
+++ b/app/src/main/res/values/values.xml
@@ -22,6 +22,7 @@
     <string name="settings_general_default_base_url_key" translatable="false">DefaultBaseURL</string>
     <string name="settings_general_users_key" translatable="false">ManageUsers</string>
     <string name="settings_general_dark_mode_key" translatable="false">DarkMode</string>
+    <string name="settings_general_datetime_format_key" translatable="false">DateTimeFormat</string>
     <string name="settings_general_language_key" translatable="false">Language</string>
     <string name="settings_general_dynamic_colors_key" translatable="false">DynamicColors</string>
     <string name="settings_general_message_bar_key" translatable="false">MessageBarEnabled</string>
@@ -208,4 +209,12 @@
         <item>1</item>
         <item>2</item>
     </string-array>
+    <string-array name="settings_general_datetime_format_entries">
+        <item>@string/settings_general_datetime_format_entry_locale</item>
+        <item>@string/settings_general_datetime_format_entry_iso8601</item>
+    </string-array>
+    <string-array name="settings_general_datetime_format_values">
+        <item>locale</item>
+        <item>iso8601</item>
+    </string-array>
 </resources>
diff --git a/app/src/main/res/xml/main_preferences.xml b/app/src/main/res/xml/main_preferences.xml
index 1ef47d3ed..f8b451bf3 100644
--- a/app/src/main/res/xml/main_preferences.xml
+++ b/app/src/main/res/xml/main_preferences.xml
@@ -54,6 +54,12 @@
                 app:entries="@array/settings_general_dark_mode_entries"
                 app:entryValues="@array/settings_general_dark_mode_values"
                 app:defaultValue="-1"/>
+        <ListPreference
+                app:key="@string/settings_general_datetime_format_key"
+                app:title="@string/settings_general_datetime_format_title"
+                app:entries="@array/settings_general_datetime_format_entries"
+                app:entryValues="@array/settings_general_datetime_format_values"
+                app:defaultValue="locale"/>
         <SwitchPreferenceCompat
                 app:key="@string/settings_general_dynamic_colors_key"
                 app:title="@string/settings_general_dynamic_colors_title"