diff --git a/LoopFollow/Charts/BGChartModel.swift b/LoopFollow/Charts/BGChartModel.swift
index 9b451ac6a..37091fb68 100644
--- a/LoopFollow/Charts/BGChartModel.swift
+++ b/LoopFollow/Charts/BGChartModel.swift
@@ -157,6 +157,7 @@ final class BGChartModel: ObservableObject {
     @Published var now: Date = .init()
     @Published var diaMarkers: [Date] = []
     @Published var midnightMarkers: [Date] = []
+    @Published var priorDayTimeMarkers: [Date] = []
     @Published var thirtyMinMark: Date? = nil
     @Published var ninetyMinMark: Date? = nil
 
@@ -179,6 +180,7 @@ final class BGChartModel: ObservableObject {
     @Published var show90Min: Bool = false
     @Published var showMidnight: Bool = false
     @Published var smallGraphTreatments: Bool = true
+    @Published var showPriorDayTime: Bool = false
 
     private static let doseFormatter: NumberFormatter = {
         let nf = NumberFormatter()
@@ -411,6 +413,7 @@ final class BGChartModel: ObservableObject {
         show90Min = Storage.shared.show90MinLine.value
         showMidnight = Storage.shared.showMidnightLines.value
         smallGraphTreatments = Storage.shared.smallGraphTreatments.value
+        showPriorDayTime = Storage.shared.showPriorDayTimeLines.value
 
         // Advanced-settings visibility toggles. The Nightscout controllers
         // collect the data regardless (it also feeds the info rows), so hidden
@@ -596,6 +599,17 @@ final class BGChartModel: ObservableObject {
             }
             return cal
         }()
+
+        // Mark the current local time on each prior day. Calendar arithmetic
+        // preserves the displayed time of day across daylight-saving changes.
+        var priorDayTimes: [Date] = []
+        var priorDayTime = calendar.date(byAdding: .day, value: -1, to: currentNow)
+        while let marker = priorDayTime, marker > domainStart {
+            priorDayTimes.append(marker)
+            priorDayTime = calendar.date(byAdding: .day, value: -1, to: marker)
+        }
+        priorDayTimeMarkers = priorDayTimes
+
         var cursor = calendar.startOfDay(for: domainStart)
         while cursor <= domainEnd {
             if cursor >= domainStart {
diff --git a/LoopFollow/Charts/BGChartView.swift b/LoopFollow/Charts/BGChartView.swift
index 9098bd123..1b7dc9407 100644
--- a/LoopFollow/Charts/BGChartView.swift
+++ b/LoopFollow/Charts/BGChartView.swift
@@ -1095,6 +1095,9 @@ private struct BGChartCanvas: View, Equatable {
             if showTreatments {
                 treatmentMarks
             }
+            if model.showPriorDayTime {
+                priorDayTimeRuleMarks
+            }
             if !isSmall {
                 ruleMarks
             } else if model.showMidnight {
@@ -1462,6 +1465,15 @@ private struct BGChartCanvas: View, Equatable {
         }
     }
 
+    @ChartContentBuilder
+    private var priorDayTimeRuleMarks: some ChartContent {
+        ForEach(model.priorDayTimeMarkers.filter { $0 >= windowStart && $0 <= windowEnd }, id: \.self) { d in
+            RuleMark(x: .value("same time on prior day", d))
+                .lineStyle(StrokeStyle(lineWidth: 1, dash: isSmall ? [2, 2] : [2, 5]))
+                .foregroundStyle(Color.orange.opacity(isSmall ? 1 : 0.5))
+        }
+    }
+
     @ChartContentBuilder
     private var ruleMarks: some ChartContent {
         RuleMark(y: .value("low", model.lowLine))
diff --git a/LoopFollow/Settings/GraphSettingsView.swift b/LoopFollow/Settings/GraphSettingsView.swift
index 07d9d8d91..7efb38c40 100644
--- a/LoopFollow/Settings/GraphSettingsView.swift
+++ b/LoopFollow/Settings/GraphSettingsView.swift
@@ -12,6 +12,7 @@ struct GraphSettingsView: View {
     @ObservedObject private var show30MinLine = Storage.shared.show30MinLine
     @ObservedObject private var show90MinLine = Storage.shared.show90MinLine
     @ObservedObject private var showMidnightLines = Storage.shared.showMidnightLines
+    @ObservedObject private var showPriorDayTimeLines = Storage.shared.showPriorDayTimeLines
     @ObservedObject private var showYesterdayLine = Storage.shared.showYesterdayLine
     @ObservedObject private var smallGraphTreatments = Storage.shared.smallGraphTreatments
 
@@ -50,6 +51,9 @@ struct GraphSettingsView: View {
 
                 Toggle("Show Midnight Lines", isOn: $showMidnightLines.value)
                     .onChange(of: showMidnightLines.value) { _ in markDirty() }
+
+                Toggle("Show Prior Day Time Lines", isOn: $showPriorDayTimeLines.value)
+                    .onChange(of: showPriorDayTimeLines.value) { _ in markDirty() }
             }
 
             // ── Treatments ───────────────────────────────────────────────
diff --git a/LoopFollow/Settings/SettingsMenuView.swift b/LoopFollow/Settings/SettingsMenuView.swift
index 38fb991fb..93fd0fd93 100644
--- a/LoopFollow/Settings/SettingsMenuView.swift
+++ b/LoopFollow/Settings/SettingsMenuView.swift
@@ -176,6 +176,7 @@ enum SettingsRoute: Hashable, Identifiable {
                 SettingsLeaf("Show −90 min Line", ["-90"]),
                 SettingsLeaf("Show Yesterday's BG", ["yesterday"]),
                 SettingsLeaf("Show Midnight Lines"),
+                SettingsLeaf("Show Prior Day Time Lines", ["prior day", "same time", "yesterday"]),
                 SettingsLeaf("Show Carb/Bolus Values", ["carbs"]),
                 SettingsLeaf("Show Carb Absorption"),
                 SettingsLeaf("Treatments on Small Graph"),
diff --git a/LoopFollow/Storage/Storage.swift b/LoopFollow/Storage/Storage.swift
index 4876924e2..32f099148 100644
--- a/LoopFollow/Storage/Storage.swift
+++ b/LoopFollow/Storage/Storage.swift
@@ -128,6 +128,7 @@ class Storage {
     var show30MinLine = StorageValue<Bool>(key: "show30MinLine", defaultValue: false)
     var show90MinLine = StorageValue<Bool>(key: "show90MinLine", defaultValue: false)
     var showMidnightLines = StorageValue<Bool>(key: "showMidnightMarkers", defaultValue: false)
+    var showPriorDayTimeLines = StorageValue<Bool>(key: "showPriorDayTimeMarkers", defaultValue: false)
     var showYesterdayLine = StorageValue<Bool>(key: "showYesterdayLine", defaultValue: false)
     var smallGraphTreatments = StorageValue<Bool>(key: "smallGraphTreatments", defaultValue: true)