diff --git a/src/lib/insights/derived/__tests__/baseline.test.ts b/src/lib/insights/derived/__tests__/baseline.test.ts
index dd30f888f..0789542ee 100644
--- a/src/lib/insights/derived/__tests__/baseline.test.ts
+++ b/src/lib/insights/derived/__tests__/baseline.test.ts
@@ -70,6 +70,50 @@ describe("pure statistics", () => {
     expect(band!.k).toBe(3);
   });
 
+  // A run of identical days has no dispersion at all: the bare MAD band
+  // collapsed to one value and every surface read "your usual range is
+  // 61–61 bpm", while a reading of 62 counted as outside it.
+  it("never collapses to a single value when the days are identical", () => {
+    const band = buildBaselineBand(Array(20).fill(61), "RESTING_HEART_RATE");
+    expect(band).not.toBeNull();
+    expect(band!.center).toBe(61);
+    expect(band!.low).toBeLessThan(61);
+    expect(band!.high).toBeGreaterThan(61);
+    // Distinct at the precision any surface prints a heart rate.
+    expect(Math.round(band!.low)).not.toBe(Math.round(band!.high));
+    // An ordinary next-day reading sits inside the band, not above it.
+    expect(62).toBeLessThanOrEqual(band!.high);
+    // The dispersion itself is reported as it is.
+    expect(band!.spread).toBe(0);
+  });
+
+  it.each([
+    ["RESTING_HEART_RATE", 61],
+    ["PULSE", 72],
+    ["HEART_RATE_VARIABILITY", 45],
+    ["RESPIRATORY_RATE", 14],
+    ["OXYGEN_SATURATION", 97],
+    ["BODY_TEMPERATURE", 36.6],
+    ["SKIN_TEMPERATURE", 34.1],
+    ["BLOOD_PRESSURE_SYS", 118],
+    ["BLOOD_PRESSURE_DIA", 76],
+    ["BLOOD_GLUCOSE", 95],
+    ["WEIGHT", 80],
+    ["VO2_MAX", 42],
+    ["ACTIVITY_STEPS", 8000],
+  ] as const)(
+    "gives %s a band that reads as a range at one decimal",
+    (type, value) => {
+      const band = buildBaselineBand(Array(10).fill(value), type);
+      expect(band!.low.toFixed(1)).not.toBe(band!.high.toFixed(1));
+    },
+  );
+
+  it("leaves a band wider than the floor exactly as the spread makes it", () => {
+    const band = buildBaselineBand([50, 52, 54, 56, 58], "PULSE", 3);
+    expect(band!.high - band!.center).toBeCloseTo(band!.spread, 10);
+  });
+
   it("parity: a composed-DAY-bucket series and the raw-DAY series yield the same band", () => {
     // Same per-day means whether they arrive as raw rows or DAY rollups.
     const perDayMeans = [60, 61, 62, 59, 63, 58, 64];
diff --git a/src/lib/insights/derived/baseline.ts b/src/lib/insights/derived/baseline.ts
index a53f5675b..4aa3ea559 100644
--- a/src/lib/insights/derived/baseline.ts
+++ b/src/lib/insights/derived/baseline.ts
@@ -34,6 +34,7 @@ import { getAgeFromDateOfBirth } from "@/lib/analytics/pulse-targets";
 import { toProfileSex } from "@/lib/profile/sex";
 import {
   clampDerivedLowerBound,
+  minimumBandHalfWidth,
   isPlausibleMetricValue,
   plausibleMetricRange,
 } from "@/lib/measurements/value-domain";
@@ -70,12 +71,13 @@ export interface VitalsBaselineValue {
   /** Robust center (median of the per-day means). */
   center: number;
   /**
-   * Band lower edge (center − k·MAD·scale), floored at 0 for a metric whose
+   * Band lower edge (center − k·MAD·scale, at least the metric's
+   * `minimumBandHalfWidth` below center), floored at 0 for a metric whose
    * plausibility domain forbids negative values. `spread` below stays the
    * unclamped dispersion, so a deviation-in-σ calculation is unaffected.
    */
   low: number;
-  /** Band upper edge (center + k·MAD·scale). */
+  /** Band upper edge (center + k·MAD·scale, with the same minimum width). */
   high: number;
   /** The MAD-derived σ-equivalent spread (k applied; same units as the metric). */
   spread: number;
@@ -204,10 +206,15 @@ export function buildBaselineBand(
   const mad = medianAbsoluteDeviation(dayMeans);
   // Scale MAD to a σ-equivalent so the band reads like a robust ±kσ.
   const spread = k * mad * MAD_SIGMA_SCALE;
+  // The edges never sit closer than the measurement's own day-to-day wobble:
+  // a run of identical days has no dispersion, and a zero-width band read
+  // "61–61 bpm" and put the next ordinary reading outside it. `spread` stays
+  // the measured dispersion for anything that reasons in σ.
+  const halfWidth = Math.max(spread, minimumBandHalfWidth(type));
   return {
     center,
-    low: clampDerivedLowerBound(type, center - spread),
-    high: center + spread,
+    low: clampDerivedLowerBound(type, center - halfWidth),
+    high: center + halfWidth,
     spread,
     sampleDays: dayMeans.length,
     k,
diff --git a/src/lib/measurements/value-domain.ts b/src/lib/measurements/value-domain.ts
index d6e485827..0f071e6f9 100644
--- a/src/lib/measurements/value-domain.ts
+++ b/src/lib/measurements/value-domain.ts
@@ -153,3 +153,35 @@ export function metricFractionDigits(type: string | null | undefined): number {
   if (type && INTEGER_VALUED_MEASUREMENT_TYPES.has(type)) return 0;
   return DEFAULT_METRIC_FRACTION_DIGITS;
 }
+
+/**
+ * The smallest half-width a personal band may have, in the metric's canonical
+ * unit: roughly the day-to-day wobble of the measurement itself.
+ *
+ * A median ± k·MAD band has no width at all when most days carry the same
+ * value (a device that reports a whole-number resting rate does this often),
+ * and then reads "your usual range is 61–61 bpm" while a reading of 62 counts
+ * as outside it. Below this width a band says nothing a single reading could
+ * not, so the band is widened to it. Metrics not listed take one step of
+ * their own display precision, which is the least that keeps the two edges
+ * apart on screen.
+ */
+const MIN_BAND_HALF_WIDTH: Readonly<Record<string, number>> = {
+  RESTING_HEART_RATE: 2, // bpm
+  PULSE: 3, // bpm
+  HEART_RATE_VARIABILITY: 3, // ms
+  RESPIRATORY_RATE: 0.5, // breaths/min
+  OXYGEN_SATURATION: 1, // %
+  BODY_TEMPERATURE: 0.2, // °C
+  SKIN_TEMPERATURE: 0.2, // °C
+  WRIST_TEMPERATURE: 0.2, // °C
+  BLOOD_PRESSURE_SYS: 4, // mmHg
+  BLOOD_PRESSURE_DIA: 3, // mmHg
+  BLOOD_GLUCOSE: 5, // mg/dL
+  WEIGHT: 0.3, // kg
+};
+
+export function minimumBandHalfWidth(type: string | null | undefined): number {
+  if (!type) return 0;
+  return MIN_BAND_HALF_WIDTH[type] ?? 10 ** -metricFractionDigits(type);
+}