diff --git a/src/__tests__/display-transform-rounding-guard.test.ts b/src/__tests__/display-transform-rounding-guard.test.ts
index f6d32f37a..8d0a4a5fd 100644
--- a/src/__tests__/display-transform-rounding-guard.test.ts
+++ b/src/__tests__/display-transform-rounding-guard.test.ts
@@ -45,8 +45,9 @@ const REGISTRY = "lib/measurements/display-transform.ts";
 /**
  * The one module allowed to import the unrounded escape hatch. The target
  * adapter needs the unrounded pound edge of a canonical guardrail so it can
- * round it INWARD — rounding to the nearest tenth first gives 66.1 lb for the
- * 30 kg floor, which inverts to 29.98 kg and the server rejects it.
+ * round it INWARD — rounding to the nearest tenth first can put the pound
+ * edge outside the kilogram window, and the server rejects what converts
+ * back from it.
  */
 const UNROUNDED_IMPORTERS = ["lib/targets/target-unit-display.ts"];
 
diff --git a/src/app/api/user/thresholds/__tests__/route.test.ts b/src/app/api/user/thresholds/__tests__/route.test.ts
index c7865e32f..6a3468a1e 100644
--- a/src/app/api/user/thresholds/__tests__/route.test.ts
+++ b/src/app/api/user/thresholds/__tests__/route.test.ts
@@ -96,7 +96,7 @@ beforeEach(() => {
 
 describe("PUT /api/user/thresholds — 422 multi-issue (v1.4.43 W6)", () => {
   it("surfaces TWO simultaneous validation errors", async () => {
-    // WEIGHT bounds are min=30, max=300. Sending min > max + a value
+    // WEIGHT bounds are min=1, max=300. Sending min > max + a value
     // out of bounds on PULSE forces two range errors.
     const res = await PUT(
       putReq({
diff --git a/src/app/insights/weight/page.tsx b/src/app/insights/weight/page.tsx
index b6685072a..75101098f 100644
--- a/src/app/insights/weight/page.tsx
+++ b/src/app/insights/weight/page.tsx
@@ -23,6 +23,7 @@ import { MetricCorrelationCard } from "@/components/insights/metric-correlation-
 import { MeasurementDiversityNudge } from "@/components/insights/measurement-diversity-nudge";
 import { MetricTargetSummary } from "@/components/insights/metric-target-summary";
 import { SubPageShell } from "@/components/insights/sub-page-shell";
+import { METRIC_BOUNDS } from "@/lib/analytics/effective-range";
 import { buildBandsFromTrafficRange } from "@/lib/analytics/value-bands";
 import { selectWeightBandRange, type WeightTargetsSlice } from "./weight-band";
 
@@ -131,7 +132,7 @@ export default function InsightsGewichtPage() {
   const weightRange = selectWeightBandRange(targets ?? null);
   const weightBands = weightRange
     ? buildBandsFromTrafficRange(weightRange, {
-        lowerBound: 30,
+        lowerBound: METRIC_BOUNDS.WEIGHT.min,
         upperBound: 250,
       })
     : undefined;
diff --git a/src/lib/analytics/__tests__/effective-range.test.ts b/src/lib/analytics/__tests__/effective-range.test.ts
index 863f00cd0..2650d4f93 100644
--- a/src/lib/analytics/__tests__/effective-range.test.ts
+++ b/src/lib/analytics/__tests__/effective-range.test.ts
@@ -1,4 +1,6 @@
 import { describe, it, expect } from "vitest";
+import { thresholdsUpdateSchema } from "@/lib/validations/thresholds";
+import { buildBandsFromTrafficRange } from "@/lib/analytics/value-bands";
 import {
   getEffectiveRange,
   getAllEffectiveRanges,
@@ -313,3 +315,37 @@ describe("resolveWeightTargetOverride", () => {
     expect(resolveWeightTargetOverride(undefined)).toBeNull();
   });
 });
+
+describe("a child's weight target", () => {
+  // A guardian keeping a record for a six-year-old sets 20 to 23 kg. The old
+  // 30 kg floor refused it with nothing but "please check your entries", and
+  // the chart's hard-coded 30 kg lower edge dropped the low red zone.
+  const child = { WEIGHT: { min: 20, max: 23 } };
+
+  it("is accepted by the same schema both save paths parse", () => {
+    expect(thresholdsUpdateSchema.safeParse(child).success).toBe(true);
+    expect(
+      thresholdsUpdateSchema.safeParse({ WEIGHT: { min: 0.5, max: 3 } })
+        .success,
+    ).toBe(false);
+  });
+
+  it("paints every band below and above the target", () => {
+    const range = getEffectiveRange(
+      "WEIGHT",
+      { heightCm: 118, dateOfBirth: null, gender: null },
+      child,
+    ).range!;
+    const bands = buildBandsFromTrafficRange(range, {
+      lowerBound: METRIC_BOUNDS.WEIGHT.min,
+      upperBound: 250,
+    });
+    expect(bands.map((band) => band.color)).toEqual([
+      "var(--destructive)",
+      "var(--warning)",
+      "var(--success)",
+      "var(--warning)",
+      "var(--destructive)",
+    ]);
+  });
+});
diff --git a/src/lib/analytics/effective-range.ts b/src/lib/analytics/effective-range.ts
index 38f02113b..0e00c6a87 100644
--- a/src/lib/analytics/effective-range.ts
+++ b/src/lib/analytics/effective-range.ts
@@ -15,6 +15,7 @@
  * consistently.
  */
 
+import { VALUE_RANGES } from "@/lib/measurements/value-ranges";
 import { binaryReferenceSex } from "@/lib/profile/sex";
 import { getBpTargets, type BpTargets } from "./bp-targets";
 import {
@@ -65,7 +66,10 @@ export const METRIC_BOUNDS: Record<
   ThresholdMetric,
   { min: number; max: number; unit: string }
 > = {
-  WEIGHT: { min: 30, max: 300, unit: "kg" },
+  // The floor is the measurement floor: a target refused for a weight the
+  // record can hold (a child's 20 kg under a 30 kg floor) left a guardian
+  // with nothing but "please check your entries".
+  WEIGHT: { min: VALUE_RANGES.WEIGHT.min, max: 300, unit: "kg" },
   BLOOD_PRESSURE_SYS: { min: 80, max: 220, unit: "mmHg" },
   BLOOD_PRESSURE_DIA: { min: 40, max: 140, unit: "mmHg" },
   PULSE: { min: 30, max: 220, unit: "bpm" },
diff --git a/src/lib/analytics/value-bands.ts b/src/lib/analytics/value-bands.ts
index 4f7cf68db..2d34febd8 100644
--- a/src/lib/analytics/value-bands.ts
+++ b/src/lib/analytics/value-bands.ts
@@ -100,10 +100,9 @@ export function buildWeightRangeFromHeight(heightCm: number): TrafficRange {
  */
 export function buildBandsFromTrafficRange(
   range: TrafficRange,
-  options: { lowerBound?: number; upperBound?: number } = {},
+  options: { lowerBound: number; upperBound: number },
 ): ValueBand[] {
-  const lowerBound = options.lowerBound ?? 30;
-  const upperBound = options.upperBound ?? 250;
+  const { lowerBound, upperBound } = options;
 
   return [
     {
@@ -139,16 +138,6 @@ export function buildBandsFromTrafficRange(
   ].filter((band) => band.max > band.min);
 }
 
-export function buildWeightBandsFromHeight(
-  heightCm: number,
-  options: { lowerBound?: number; upperBound?: number } = {},
-): ValueBand[] {
-  return buildBandsFromTrafficRange(
-    buildWeightRangeFromHeight(heightCm),
-    options,
-  );
-}
-
 /**
  * Body-fat target range — the "green" band shown on the dashboard /
  * targets page / chart value-bands.
diff --git a/src/lib/dashboard/__tests__/target-bands.test.ts b/src/lib/dashboard/__tests__/target-bands.test.ts
index a60b3eb36..1883e175d 100644
--- a/src/lib/dashboard/__tests__/target-bands.test.ts
+++ b/src/lib/dashboard/__tests__/target-bands.test.ts
@@ -10,10 +10,11 @@ import { describe, it, expect } from "vitest";
 
 import { buildTargetBands } from "../snapshot";
 import { getBpTargets } from "@/lib/analytics/bp-targets";
+import { METRIC_BOUNDS } from "@/lib/analytics/effective-range";
 import {
   buildTrafficLightBands,
   buildTrafficRange,
-  buildWeightBandsFromHeight,
+  buildBandsFromTrafficRange,
   buildWeightRangeFromHeight,
   getBodyFatTargetRange,
 } from "@/lib/analytics/value-bands";
@@ -38,8 +39,8 @@ function clientBands(profile: {
     ? buildWeightRangeFromHeight(profile.heightCm)
     : null;
   const weightBands = profile.heightCm
-    ? buildWeightBandsFromHeight(profile.heightCm, {
-        lowerBound: 30,
+    ? buildBandsFromTrafficRange(buildWeightRangeFromHeight(profile.heightCm), {
+        lowerBound: METRIC_BOUNDS.WEIGHT.min,
         upperBound: 250,
       })
     : null;
diff --git a/src/lib/dashboard/bands.ts b/src/lib/dashboard/bands.ts
index 1bfe1649d..5f03dacab 100644
--- a/src/lib/dashboard/bands.ts
+++ b/src/lib/dashboard/bands.ts
@@ -32,6 +32,7 @@ import {
 import { binaryReferenceSex, type ProfileSex } from "@/lib/profile/sex";
 import {
   getEffectiveRange,
+  METRIC_BOUNDS,
   resolveEffectiveBpTargets,
   resolveThresholdOverride,
   type ThresholdMetric,
@@ -136,7 +137,7 @@ export function buildDashboardBands(profile: {
     (profile.heightCm ? buildWeightRangeFromHeight(profile.heightCm) : null);
   const weightBands = weightRange
     ? buildBandsFromTrafficRange(weightRange, {
-        lowerBound: 30,
+        lowerBound: METRIC_BOUNDS.WEIGHT.min,
         upperBound: 250,
       })
     : null;
diff --git a/src/lib/targets/__tests__/target-unit-display.test.ts b/src/lib/targets/__tests__/target-unit-display.test.ts
index 3d2fa1522..590ce8063 100644
--- a/src/lib/targets/__tests__/target-unit-display.test.ts
+++ b/src/lib/targets/__tests__/target-unit-display.test.ts
@@ -28,7 +28,7 @@ describe("resolveTargetUnitAdapter — metric account (identity)", () => {
       expect(units.toCanonical(value)).toBe(value);
       expect(units.toDisplayDelta(value)).toBe(value);
     }
-    expect(units.bounds(METRIC_BOUNDS.WEIGHT)).toEqual({ min: 30, max: 300 });
+    expect(units.bounds(METRIC_BOUNDS.WEIGHT)).toEqual({ min: 1, max: 300 });
     expect(units.step).toBe(0.1);
   });
 
@@ -115,9 +115,9 @@ describe("resolveTargetUnitAdapter — imperial weight class", () => {
 
   it("rounds guardrails inward so a value typed at the limit still saves", () => {
     const bounds = units.bounds(METRIC_BOUNDS.WEIGHT);
-    // A naive round of the 30 kg floor gives 66.1 lb, which inverts to
-    // 29.98 kg and the server rejects it. The ceiling keeps it legal.
-    expect(bounds.min).toBe(66.2);
+    // The 1 kg floor is 2.2046 lb: the floor rounds up to 2.3, never down,
+    // so a value typed at the limit converts back inside the window.
+    expect(bounds.min).toBe(2.3);
     expect(bounds.max).toBe(661.3);
     expect(units.toCanonical(bounds.min)).toBeGreaterThanOrEqual(
       METRIC_BOUNDS.WEIGHT.min,
@@ -144,7 +144,7 @@ describe("resolveTargetUnitAdapter — imperial weight class", () => {
 
   it("still rejects a genuinely out-of-range value", () => {
     const bounds = units.bounds(METRIC_BOUNDS.WEIGHT);
-    for (const typed of [12, 66.1, 661.4, 900]) {
+    for (const typed of [0.5, 2.2, 661.4, 900]) {
       expect(typed < bounds.min || typed > bounds.max).toBe(true);
     }
   });
diff --git a/src/lib/targets/target-unit-display.ts b/src/lib/targets/target-unit-display.ts
index 0afb78a7d..e1d3fd6c6 100644
--- a/src/lib/targets/target-unit-display.ts
+++ b/src/lib/targets/target-unit-display.ts
@@ -27,7 +27,7 @@
  *      68.04 kg, not 68.03885550000001.
  *   3. Rules 1 + 2 compose back to the typed number: 150 lb → 68.04 kg
  *      → 150 lb. Save-then-reopen is stable.
- *   4. Guardrails round INWARD (min up, max down). A naive round of the
+ *   4. Guardrails round INWARD (min up, max down). A naive round of a
  *      30 kg floor gives 66.1 lb, which inverts to 29.98 kg and the
  *      server rejects it. Ceiling it to 66.2 lb inverts to 30.03 kg and
  *      passes.
@@ -205,8 +205,8 @@ export function resolveTargetUnitAdapter(
       applyDisplayTransformDelta(canonicalDelta, transform),
     // A guardrail is not a rendered value — it is the window a typed
     // number is checked against, and it has to round INWARD (rule 4).
-    // That needs the UNROUNDED edge: the shared helper would round 30 kg
-    // to 66.1 lb first and the ceiling below would then be a no-op on an
+    // That needs the UNROUNDED edge: the shared helper would round a 30 kg
+    // floor to 66.1 lb first and the ceiling below would then be a no-op on an
     // edge that already inverts to 29.98 kg.
     bounds: (canonical) => ({
       min: ceilTo(