[syncfusion_flutter_charts] Switching to or from DST breaks daily or weekly labels

[DrNiels]

Bug description

Using the charts to display a timespan during which a switch to or from DST occurs computes the ticks after the change wrong, either an hour to early or too late. This happens due to the implementation of _nextData in datetime_axis.dart. For the interval type week or day a duration is added. Durations in turn assume a day to have 24 hours, which is not correct during the change, as days are 23 or 25 hours long on this special occasion. You can find a suggested fix here: DrNiels@53307f3

Steps to reproduce

1. Set your timezone to Germany/Berlin
2. Load the code sample
3. Check the axis

Code sample

Code sample

import 'package:flutter/material.dart';
import 'package:syncfusion_flutter_charts/charts.dart';

void main() {
  return runApp(_ChartApp());
}

class _ChartApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(primarySwatch: Colors.blue, useMaterial3: false),
      home: _MyHomePage(),
    );
  }
}

class _MyHomePage extends StatefulWidget {
  // ignore: prefer_const_constructors_in_immutables
  _MyHomePage({Key? key}) : super(key: key);

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<_MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Syncfusion Flutter chart')),
      body: SfCartesianChart(
        primaryXAxis: DateTimeAxis(
          minimum: DateTime(2025, 10, 25),
          maximum: DateTime(2025, 10, 28),
          intervalType: DateTimeIntervalType.days,
        ),
        // Chart title
        title: ChartTitle(text: 'Half yearly sales analysis'),
        // Enable legend
        legend: Legend(isVisible: true),
        // Enable tooltip
        tooltipBehavior: TooltipBehavior(enable: true),
        series: <CartesianSeries<_SalesData, String>>[
        ],
      ),
    );
  }
}

class _SalesData {
  _SalesData(this.year, this.sales);

  final String year;
  final double sales;
}

Screenshots or Video

Screenshots / Video demonstration

Without fix:

With fix:

Stack Traces

Stack Traces

Not applicable

On which target platforms have you observed this bug?

Web, Android, Windows

Flutter Doctor output

Doctor output

[√] Flutter (Channel stable, 3.32.0, on Microsoft Windows [Version 10.0.19045.6456], locale de-DE) [574ms]
    • Flutter version 3.32.0 on channel stable at C:\Users\Niels\Documents\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision be698c48a6 (6 months ago), 2025-05-19 12:59:14 -0700
    • Engine revision 1881800949
    • Dart version 3.8.0
    • DevTools version 2.45.1

[√] Windows Version (10 Education 64-bit, 22H2, 2009) [2,5s]

[!] Android toolchain - develop for Android devices (Android SDK version 35.0.0) [5,8s]
    • Android SDK at C:\Users\Niels\AppData\Local\Android\Sdk
    • Platform android-35, build-tools 35.0.0
    • Java binary at: C:\Program Files\Android\Android Studio1\jbr\bin\java
      This is the JDK bundled with the latest Android Studio installation on this machine.
      To manually set the JDK path, use: `flutter config --jdk-dir="path/to/jdk"`.
    • Java version OpenJDK Runtime Environment (build 17.0.11+0--11852314)
    ! Some Android licenses not accepted. To resolve this, run: flutter doctor --android-licenses

[√] Chrome - develop for the web [116ms]
    • Chrome at C:\Users\Niels\AppData\Local\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.14.15 (September 2025)) [115ms]
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
    • Visual Studio Community 2022 version 17.14.36511.14
    • Windows 10 SDK version 10.0.26100.0

[!] Android Studio (version 2021.2) [28ms]
    • Android Studio at C:\Program Files\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    X Unable to determine bundled Java version.
    • Try updating or re-installing Android Studio.

[√] Android Studio (version 2024.1) [26ms]
    • Android Studio at C:\Program Files\Android\Android Studio1
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.11+0--11852314)

[√] VS Code, 64-bit edition (version 1.104.2) [25ms]
    • VS Code at C:\Program Files\Microsoft VS Code
    • Flutter extension version 3.122.0

[√] Connected device (4 available) [563ms]
    • SM S921B (wireless) (mobile) • adb-RFCX306GLHZ-2OV7MI._adb-tls-connect._tcp. • android-arm64  • Android 16 (API 36)
    • Windows (desktop)            • windows                                       • windows-x64    • Microsoft Windows [Version 10.0.19045.6456]
    • Chrome (web)                 • chrome                                        • web-javascript • Google Chrome 142.0.7444.59
    • Edge (web)                   • edge                                          • web-javascript • Microsoft Edge 128.0.2739.42

[√] Network resources [703ms]
    • All expected network resources are available.

! Doctor found issues in 2 categories.

[Harsha-SF4223]

Hi DrNiels,

We appreciate your contribution and have reviewed your suggested fix. However, we’d like to clarify that the duplicate label is caused by the Daylight-Saving Time change in the Germany/Berlin time zone, where clocks moved back one hour. This creates two distinct timestamps on the same date, leading to duplicate axis labels. To avoid this case, you can format the axis labels using UTC time to avoid local time zone effects using the axisLabelFormatter. If your requirement aligns with this approach, you can use and customize the workaround sample based on your needs.

primaryXAxis: DateTimeAxis(
  axisLabelFormatter: (axisLabelRenderArgs) {

    final utcTime = DateTime.fromMillisecondsSinceEpoch(

      axisLabelRenderArgs.value.toInt(),

      isUtc: true,

    );

    final istTime = utcTime.add(const Duration(hours: 5, minutes: 30));

    final formattedText = DateFormat('dd').format(istTime);

    return ChartAxisLabel(formattedText, axisLabelRenderArgs.textStyle);

  },

Also, we have already logged a feature request to add timezone support in SfCartesianChart in our Feedback Portal and this feature will be available in any of our upcoming release. You can track the status of this request through the provided feedback link. We will also consider your case in our implementation.

FR link: Time zone support for SfCartesianChart in Flutter | Feedback Portal

Regards,
Harsha.

[DrNiels]

The issue is not with the label formatter but with the tick position. The current implementation always adds a duration of one day, which is always 24 hours. However, when changing from or to DST, the assumption of 24 hours a day is wrong. Consider my screenshot. The second tick is captioned Oct 26. It's precise DateTime is Oct 26 at 00:00:00. The next tick is also labelled Oct 26, but is actually Oct 26 at 23:00:00 because that's 24 hours after 00:00:00. Nonetheless, a daily intervall should show Oct 27 at 00:00:00, even though that's 25 hours later.

Other intervals actually already work great during the change of DST and I wouldn't want to miss those features by sticking to UTC. When leaving DST, an hourly interval shows 2:00 two times (as the clock is reset two 2:00 at 3:00 and thus that time occurs two times) and when entering DST 2:00 is not shown at all (as the clock is forwarded from 2:00 to 3:00, skipping the hour).

As the provided fix is sufficient for my use case, feel free to use or discard that feedback as you want.

[Harsha-SF4223]

Hi DrNiels,

Thank you for sharing your detailed feedback. As mentioned in our previous update, we have already logged a feature request for time zone support in our chart. Your case highlights an important scenario, and we will review your suggestion with our development team during the implementation of this feature. If feasible, we will incorporate your approach or a similar solution to ensure accurate tick positioning during DST changes.

If you would like to show your support for this feature, we encourage you to add your vote using the link below:
FR Link: https://www.syncfusion.com/feedback/62812/time-zone-support-for-sfcartesianchart

Regards,
Harsha.