diff --git a/web/src/app/charging/page.tsx b/web/src/app/charging/page.tsx
index 0f0c9c6..16f8279 100644
--- a/web/src/app/charging/page.tsx
+++ b/web/src/app/charging/page.tsx
@@ -57,6 +57,7 @@ export default async function ChargingPage() {
                     <div>
                       <div className="session-when">{dateTime(session.startedAt)}</div>
                       <div className="session-meta">
+                        {session.isDemo && "Demo · "}
                         {duration(session.durationSeconds)}
                         {gained !== null && ` · %${num(session.startSocPercent as number)} → %${num(session.endSocPercent as number)}`}
                       </div>
diff --git a/web/src/lib/mongo.ts b/web/src/lib/mongo.ts
index 4bac775..230422c 100644
--- a/web/src/lib/mongo.ts
+++ b/web/src/lib/mongo.ts
@@ -45,6 +45,7 @@ export interface ChargingSession {
   gridEnergyKwh: number;
   pricePerKwh: number;
   totalCost: number;
+  isDemo?: boolean;
   startSocPercent?: number;
   endSocPercent?: number;
   curve: CurvePoint[];
diff --git a/web/src/lib/validate.ts b/web/src/lib/validate.ts
index 333a916..2f9447a 100644
--- a/web/src/lib/validate.ts
+++ b/web/src/lib/validate.ts
@@ -49,6 +49,7 @@ export function validateChargingSession(body: unknown, pathSessionId: string): C
   });
   const startSocPercent = record.startSocPercent;
   const endSocPercent = record.endSocPercent;
+  const isDemo = record.isDemo;
   const energyKwh = bounded(record.energyKwh, 0, 1000, "energyKwh");
   const pricePerKwh = bounded(record.pricePerKwh, 0, 1_000_000, "pricePerKwh");
   const chargingLossPercent = 10;
@@ -64,6 +65,7 @@ export function validateChargingSession(body: unknown, pathSessionId: string): C
     gridEnergyKwh,
     pricePerKwh,
     totalCost: gridEnergyKwh * pricePerKwh,
+    ...(isDemo === true ? { isDemo: true } : {}),
     ...(startSocPercent === undefined ? {} : { startSocPercent: bounded(startSocPercent, 0, 100, "startSocPercent") }),
     ...(endSocPercent === undefined ? {} : { endSocPercent: bounded(endSocPercent, 0, 100, "endSocPercent") }),
     curve,
diff --git a/web/test/validate.test.ts b/web/test/validate.test.ts
index ab1144c..eeef907 100644
--- a/web/test/validate.test.ts
+++ b/web/test/validate.test.ts
@@ -56,6 +56,7 @@ test("a charging session must match the id in its path", () => {
     gridEnergyKwh: 34.54,
     pricePerKwh: 7.5,
     totalCost: 235.5,
+    isDemo: true,
     startSocPercent: 18,
     endSocPercent: 72,
     curve: [{ timestampMs: 1_760_000_060_000, powerKw: 84.2, socPercent: 20 }],
@@ -66,6 +67,7 @@ test("a charging session must match the id in its path", () => {
   assert.equal(record.chargingLossPercent, 10);
   assert.equal(record.gridEnergyKwh, 34.54);
   assert.equal(record.totalCost, 259.05);
+  assert.equal(record.isDemo, true);
   assert.throws(() => validateChargingSession(body, "11111111-2222-4333-8444-555555555556"), ValidationError);
 });