diff --git a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/WorkingHoursExcelExportE2ETests.cs b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/WorkingHoursExcelExportE2ETests.cs
index 7708b9c4..3418f40b 100644
--- a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/WorkingHoursExcelExportE2ETests.cs
+++ b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn.Test/WorkingHoursExcelExportE2ETests.cs
@@ -1,4 +1,5 @@
 using System;
+using System.Globalization;
 using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
@@ -139,6 +140,219 @@ await SeedSiteAndPlanRegistration(
         Assert.That(shift1Stop, Is.EqualTo("10:00"), "Legacy slot 121 → Options[120] = \"10:00\"");
     }
 
+    /// <summary>
+    /// Regression coverage for the read-time flex chain (<c>ApplyRunningFlexChain</c>
+    /// in <c>TimePlanningWorkingHoursService</c>) failing to deduct a paid-out flex
+    /// on <c>UseOneMinuteIntervals=true</c> sites. Production writers (e.g. the
+    /// "set flex" flow, <c>TimePlanningFlexService.UpdatePlanning</c>) only ever
+    /// populate the legacy double <c>PaiedOutFlex</c>; <c>PaiedOutFlexInSeconds</c>
+    /// stays at its unpopulated default of 0 unless the caller sets it explicitly.
+    /// Pre-fix, the chain subtracted <c>PaiedOutFlexInSeconds</c> with no fallback,
+    /// so 2h flex with 30min paid out rendered as 2h (undeducted) instead of 1.5h.
+    /// </summary>
+    [Test]
+    public async Task Index_FlagOn_PaiedOutFlexInSecondsZero_FallsBackToPaidOutFlexDouble()
+    {
+        await SeedFlexScenario(
+            siteUid: 9703,
+            date: new DateTime(2026, 5, 17),
+            flexInSecondsOnTargetDay: 7200, // 2h flex
+            paiedOutFlexOnTargetDay: 0.5, // 30 min paid out — legacy double only
+            paiedOutFlexInSecondsOnTargetDay: 0);
+
+        var result = await _service.Index(new TimePlanningWorkingHoursRequestModel
+        {
+            SiteId = 9703,
+            DateFrom = new DateTime(2026, 5, 16),
+            DateTo = new DateTime(2026, 5, 17),
+        });
+
+        Assert.That(result.Success, Is.True, result.Message);
+        var targetRow = result.Model!.Single(r => r.Date == new DateTime(2026, 5, 17));
+
+        // 2h flex - 30min paid out = 1.5h (5400s). Pre-fix this read 2h (7200s)
+        // because PaiedOutFlexInSeconds (always 0 from production writers) was
+        // subtracted directly with no fallback to the populated double.
+        Assert.That(targetRow.SumFlexEndInSeconds, Is.EqualTo(5400));
+        Assert.That(targetRow.SumFlexEnd, Is.EqualTo(1.5).Within(0.001));
+    }
+
+    /// <summary>
+    /// When <c>PaiedOutFlexInSeconds</c> IS populated (e.g. a future writer that
+    /// keeps it in sync), that value must win over the double-derived fallback —
+    /// mirrors <c>PlanRegistrationHelperTests.SumFlex_FlagOn_PaiedOutFlexInSecondsZero_FallsBackToPaiedOutFlex</c>'s
+    /// counterpart case for the write-time chain.
+    /// </summary>
+    [Test]
+    public async Task Index_FlagOn_PaiedOutFlexInSecondsSet_UsesStoredSecondsOverDouble()
+    {
+        await SeedFlexScenario(
+            siteUid: 9704,
+            date: new DateTime(2026, 5, 18),
+            flexInSecondsOnTargetDay: 7200, // 2h flex
+            paiedOutFlexOnTargetDay: 0.5, // legacy double says 30 min...
+            paiedOutFlexInSecondsOnTargetDay: 900); // ...but the seconds column says 15 min; that must win.
+
+        var result = await _service.Index(new TimePlanningWorkingHoursRequestModel
+        {
+            SiteId = 9704,
+            DateFrom = new DateTime(2026, 5, 17),
+            DateTo = new DateTime(2026, 5, 18),
+        });
+
+        Assert.That(result.Success, Is.True, result.Message);
+        var targetRow = result.Model!.Single(r => r.Date == new DateTime(2026, 5, 18));
+
+        // 2h flex - 15min (the populated *InSeconds* column) = 1h45m (6300s).
+        Assert.That(targetRow.SumFlexEndInSeconds, Is.EqualTo(6300));
+        Assert.That(targetRow.SumFlexEnd, Is.EqualTo(1.75).Within(0.001));
+    }
+
+    [Test]
+    public async Task GenerateExcelDashboard_FlagOn_PaiedOutFlexSet_SumFlexEndCellDeductsIt()
+    {
+        await SeedFlexScenario(
+            siteUid: 9705,
+            date: new DateTime(2026, 5, 19),
+            flexInSecondsOnTargetDay: 7200, // 2h flex
+            paiedOutFlexOnTargetDay: 0.5, // 30 min paid out — legacy double only
+            paiedOutFlexInSecondsOnTargetDay: 0);
+
+        var result = await _service.GenerateExcelDashboard(new TimePlanningWorkingHoursRequestModel
+        {
+            SiteId = 9705,
+            DateFrom = new DateTime(2026, 5, 19),
+            DateTo = new DateTime(2026, 5, 19),
+        });
+
+        Assert.That(result.Success, Is.True, result.Message);
+        Assert.That(result.Model, Is.Not.Null);
+
+        var (sumFlexEnd, paidOutFlex) = ReadFlexCells(result.Model!);
+        Assert.That(double.Parse(sumFlexEnd, CultureInfo.InvariantCulture), Is.EqualTo(1.5).Within(0.001),
+            "SumFlexEnd column must reflect Flex minus PaiedOutFlex, not the raw Flex total " +
+            "(regression lock for the read-time chain fallback fix)");
+        Assert.That(double.Parse(paidOutFlex, CultureInfo.InvariantCulture), Is.EqualTo(0.5).Within(0.001));
+    }
+
+    /// <summary>
+    /// Seeds an SDK Site/Worker + UseOneMinuteIntervals=true AssignedSite + a
+    /// neutral prior-day PlanRegistration (so the running SumFlexStart chain
+    /// enters the target day at exactly 0) + a target-day PlanRegistration
+    /// carrying the exact production shape of the PaiedOutFlex bug: FlexInSeconds
+    /// set, the legacy double PaiedOutFlex set, and PaiedOutFlexInSeconds left at
+    /// whatever the caller passes (0 = the value every production writer leaves it at).
+    /// </summary>
+    private async Task SeedFlexScenario(
+        int siteUid, DateTime date,
+        int flexInSecondsOnTargetDay, double paiedOutFlexOnTargetDay, int paiedOutFlexInSecondsOnTargetDay)
+    {
+        var core = await GetCore();
+        var sdkDb = core.DbContextHelper.GetDbContext();
+
+        var site = new SdkSite { Name = $"Site {siteUid}", MicrotingUid = siteUid };
+        await site.Create(sdkDb);
+
+        var worker = new SdkWorker
+        {
+            FirstName = "Test",
+            LastName = "Worker",
+            Email = $"test{siteUid}@example.com",
+            MicrotingUid = 1000 + siteUid,
+        };
+        await worker.Create(sdkDb);
+
+        var siteWorker = new SdkSiteWorker
+        {
+            SiteId = site.Id,
+            WorkerId = worker.Id,
+            MicrotingUid = 2000 + siteUid,
+        };
+        await siteWorker.Create(sdkDb);
+
+        await new AssignedSiteEntity
+        {
+            SiteId = siteUid,
+            UseOneMinuteIntervals = true,
+            WorkflowState = Constants.WorkflowStates.Created,
+            CreatedByUserId = 1,
+            UpdatedByUserId = 1,
+        }.Create(TimePlanningPnDbContext!);
+
+        await new PlanRegistrationEntity
+        {
+            SdkSitId = siteUid,
+            Date = date.AddDays(-1),
+            Start1Id = 0,
+            Stop1Id = 0,
+            Pause1Id = 0,
+            PlanText = "",
+            CommentOffice = "",
+            CommentOfficeAll = "",
+            WorkflowState = Constants.WorkflowStates.Created,
+            CreatedByUserId = 1,
+            UpdatedByUserId = 1,
+        }.Create(TimePlanningPnDbContext!);
+
+        await new PlanRegistrationEntity
+        {
+            SdkSitId = siteUid,
+            Date = date,
+            Start1Id = 0,
+            Stop1Id = 0,
+            Pause1Id = 0,
+            FlexInSeconds = flexInSecondsOnTargetDay,
+            PaiedOutFlex = paiedOutFlexOnTargetDay,
+            PaiedOutFlexInSeconds = paiedOutFlexInSecondsOnTargetDay,
+            PlanText = "",
+            CommentOffice = "",
+            CommentOfficeAll = "",
+            WorkflowState = Constants.WorkflowStates.Created,
+            CreatedByUserId = 1,
+            UpdatedByUserId = 1,
+        }.Create(TimePlanningPnDbContext!);
+    }
+
+    /// <summary>
+    /// Reads the (SumFlexEnd, PaidOutFlex) cell text from the first data row that
+    /// has either populated. Column layout from <c>FillDataRow</c> when
+    /// Third/Fourth/FifthShiftActive are all off (0-indexed): ...14=NettoHours,
+    /// 15=FlexHours, 16=SumFlexEnd, 17=PaidOutFlex(numeric), 18=Message, ...
+    /// </summary>
+    private static (string SumFlexEnd, string PaidOutFlex) ReadFlexCells(Stream xlsx)
+    {
+        xlsx.Position = 0;
+        using var doc = SpreadsheetDocument.Open(xlsx, false);
+        var workbookPart = doc.WorkbookPart!;
+        var dashboardSheet = workbookPart.Workbook.Descendants<Sheet>()
+            .First(s => s.Name == "Dashboard");
+        var dashboardPart = (WorksheetPart)workbookPart.GetPartById(dashboardSheet.Id!);
+        var sheet = dashboardPart.Worksheet;
+        var sst = workbookPart.SharedStringTablePart?.SharedStringTable;
+        string CellText(Cell c)
+        {
+            var raw = c.CellValue?.Text ?? c.InnerText ?? "";
+            if (c.DataType?.Value == CellValues.SharedString && sst != null && int.TryParse(raw, out var idx))
+            {
+                return sst.ElementAt(idx).InnerText;
+            }
+            return raw;
+        }
+        var rows = sheet.Descendants<Row>().ToList();
+        foreach (var row in rows.Where(r => r.RowIndex == null || r.RowIndex! > 1U))
+        {
+            var cells = row.Elements<Cell>().ToList();
+            if (cells.Count < 18) continue;
+            var sumFlexEnd = CellText(cells[16]);
+            var paidOutFlex = CellText(cells[17]);
+            if (!string.IsNullOrEmpty(sumFlexEnd) || !string.IsNullOrEmpty(paidOutFlex))
+            {
+                return (sumFlexEnd, paidOutFlex);
+            }
+        }
+        return ("", "");
+    }
+
     private async Task SeedSiteAndPlanRegistration(
         int siteUid, DateTime date, bool useOneMinuteIntervals,
         DateTime? start1, DateTime? stop1,
diff --git a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningFlexService/TimePlanningFlexService.cs b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningFlexService/TimePlanningFlexService.cs
index 66ee2507..dfdcb8dd 100644
--- a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningFlexService/TimePlanningFlexService.cs
+++ b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningFlexService/TimePlanningFlexService.cs
@@ -247,8 +247,22 @@ private async Task UpdatePlanning(PlanRegistration planRegistration,
     {
         planRegistration.CommentOfficeAll = model.CommentOfficeAll;
         planRegistration.CommentOffice = model.CommentOffice;
+
+        // PaiedOutFlexInSeconds is the source the flag-on flex chain
+        // (PlanRegistrationHelper.ApplyNettoFlexChainSecondPrecision /
+        // TimePlanningWorkingHoursService.ApplyRunningFlexChain) subtracts. Only ever
+        // updating the legacy double below would leave that column stale, so keep it
+        // in lockstep here too. Old value falls back to the double the same way those
+        // chains do, since this row may itself have only ever had the double set.
+        var oldPaiedOutFlexSeconds = planRegistration.PaiedOutFlexInSeconds != 0
+            ? planRegistration.PaiedOutFlexInSeconds
+            : (int)Math.Round(planRegistration.PaiedOutFlex * 3600);
+        var newPaiedOutFlexSeconds = (int)Math.Round(model.PaidOutFlex * 3600);
+
         planRegistration.SumFlexEnd += planRegistration.PaiedOutFlex - model.PaidOutFlex;
+        planRegistration.SumFlexEndInSeconds += oldPaiedOutFlexSeconds - newPaiedOutFlexSeconds;
         planRegistration.PaiedOutFlex = model.PaidOutFlex;
+        planRegistration.PaiedOutFlexInSeconds = newPaiedOutFlexSeconds;
         planRegistration.UpdatedByUserId = userService.UserId;
 
         await planRegistration.Update(dbContext);
diff --git a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningWorkingHoursService/TimePlanningWorkingHoursService.cs b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningWorkingHoursService/TimePlanningWorkingHoursService.cs
index b666020d..ed82fbd4 100644
--- a/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningWorkingHoursService/TimePlanningWorkingHoursService.cs
+++ b/eFormAPI/Plugins/TimePlanning.Pn/TimePlanning.Pn/Services/TimePlanningWorkingHoursService/TimePlanningWorkingHoursService.cs
@@ -958,6 +958,26 @@ public async Task<OperationDataResult<TimePlanningHoursSummaryModel>> CalculateH
     }
 
 
+    /// <summary>
+    /// Production writers (e.g. <c>TimePlanningFlexService.UpdatePlanning</c>) only
+    /// ever populate the legacy double <c>PaiedOutFlex</c>/<c>PaidOutFlex</c> fields;
+    /// <c>PaiedOutFlexInSeconds</c> stays at its default of 0. Mirrors the identical
+    /// fallback in <see cref="PlanRegistrationHelper.ApplyNettoFlexChainSecondPrecision"/>
+    /// so the flag-on chain doesn't silently treat a real paid-out flex as zero.
+    /// </summary>
+    private static int PaiedOutFlexSecondsWithFallback(TimePlanningWorkingHoursModel model)
+    {
+        if (model.PaiedOutFlexInSeconds != 0)
+        {
+            return model.PaiedOutFlexInSeconds;
+        }
+
+        return string.IsNullOrEmpty(model.PaidOutFlex)
+            ? 0
+            : (int)Math.Round(
+                double.Parse(model.PaidOutFlex.Replace(",", "."), CultureInfo.InvariantCulture) * 3600);
+    }
+
     /// <summary>
     /// Applies the running flex-balance chain over an ordered-by-date list of
     /// working-hours rows. Single source of truth for the flex balance rendered
@@ -992,7 +1012,7 @@ private void ApplyRunningFlexChain(
                     timePlanningWorkingHoursModel.SumFlexEndInSeconds =
                         timePlanningWorkingHoursModel.SumFlexStartInSeconds
                         + timePlanningWorkingHoursModel.FlexInSeconds
-                        - timePlanningWorkingHoursModel.PaiedOutFlexInSeconds;
+                        - PaiedOutFlexSecondsWithFallback(timePlanningWorkingHoursModel);
                     timePlanningWorkingHoursModel.SumFlexEnd =
                         timePlanningWorkingHoursModel.SumFlexEndInSeconds / 3600.0;
                     sumFlexEndInSeconds = timePlanningWorkingHoursModel.SumFlexEndInSeconds;
@@ -1022,7 +1042,7 @@ private void ApplyRunningFlexChain(
                         timePlanningWorkingHoursModel.SumFlexEndInSeconds =
                             timePlanningWorkingHoursModel.SumFlexStartInSeconds
                             + timePlanningWorkingHoursModel.FlexInSeconds
-                            - timePlanningWorkingHoursModel.PaiedOutFlexInSeconds;
+                            - PaiedOutFlexSecondsWithFallback(timePlanningWorkingHoursModel);
                         timePlanningWorkingHoursModel.SumFlexEnd =
                             timePlanningWorkingHoursModel.SumFlexEndInSeconds / 3600.0;
                     }