diff --git a/apps/portal/src/lib/components/PlayersTable.svelte b/apps/portal/src/lib/components/PlayersTable.svelte
index 4109dd0..911e641 100644
--- a/apps/portal/src/lib/components/PlayersTable.svelte
+++ b/apps/portal/src/lib/components/PlayersTable.svelte
@@ -1,5 +1,6 @@
 <script lang="ts">
     import { onMount } from "svelte";
+    import { beforeNavigate } from "$app/navigation";
     import {
         LevelCalculator,
         type LevelCalculatorOutput,
@@ -26,12 +27,30 @@
         levels?: LevelCalculatorOutput;
         player: Player;
         activityPerformances: ActivityPerformance[];
+        /** JSON snapshot of {player, activityPerformances} as of the last successful save/load. "" means never saved. */
+        savedSnapshot: string;
         saving?: boolean;
         saveError?: string;
         deleting?: boolean;
         deleteError?: string;
     }
 
+    function snapshotOf(
+        player: Player,
+        activityPerformances: ActivityPerformance[],
+    ): string {
+        return JSON.stringify({ player, activityPerformances });
+    }
+
+    function isDirty(calculation: CalcData): boolean {
+        return (
+            snapshotOf(
+                calculation.player,
+                calculation.activityPerformances,
+            ) !== calculation.savedSnapshot
+        );
+    }
+
     interface Props {
         allStandards: Standards;
     }
@@ -54,21 +73,25 @@
     } as const satisfies Record<Activity, keyof AssessmentRow>;
 
     function assessmentToCalc(assessment: AssessmentRow): CalcData {
+        const player: Player = {
+            name: assessment.name,
+            metrics: {
+                age: assessment.age,
+                weight: assessment.weight,
+                gender: assessment.gender as Gender,
+            },
+        };
+        const activityPerformances = Object.values(Activity).map((a) => ({
+            activity: a,
+            performance: (assessment[PERF_COLUMN[a]] as number | null) ?? 0,
+        }));
+
         return {
             key: crypto.randomUUID(),
             id: assessment.id,
-            player: {
-                name: assessment.name,
-                metrics: {
-                    age: assessment.age,
-                    weight: assessment.weight,
-                    gender: assessment.gender as Gender,
-                },
-            },
-            activityPerformances: Object.values(Activity).map((a) => ({
-                activity: a,
-                performance: (assessment[PERF_COLUMN[a]] as number | null) ?? 0,
-            })),
+            player,
+            activityPerformances,
+            savedSnapshot: snapshotOf(player, activityPerformances),
         };
     }
 
@@ -104,6 +127,10 @@
             });
             if (res.error) throw res.error;
             calculation.id = res.data?.id;
+            calculation.savedSnapshot = snapshotOf(
+                calculation.player,
+                calculation.activityPerformances,
+            );
         } catch (err) {
             calculation.saveError = errorMessage(err);
         } finally {
@@ -132,6 +159,24 @@
 
     onMount(loadAssessments);
 
+    beforeNavigate((navigation) => {
+        if (!calculations.some(isDirty)) return;
+
+        if (navigation.type === "leave") {
+            // triggers the browser's native "leave site?" confirmation
+            navigation.cancel();
+            return;
+        }
+
+        if (
+            !confirm(
+                "You have unsaved player changes that will be lost. Leave anyway?",
+            )
+        ) {
+            navigation.cancel();
+        }
+    });
+
     $effect(() => {
         for (const calculation of calculations) {
             calculation.levels = levelCalculator.calculate(
@@ -144,6 +189,7 @@
     const createCalculation = function (name: string): CalcData {
         return {
             key: crypto.randomUUID(),
+            savedSnapshot: "", // never saved — always dirty until the first save
             player: {
                 name: name,
                 metrics: {
@@ -260,12 +306,19 @@
             class="card card-compact bg-base-200 p-4 shadow-lg max-w-sm w-full"
         >
             <div class="card-body gap-4 p-4">
-                <input
-                    class="input input-bordered input-sm w-full"
-                    type="text"
-                    bind:value={calculation.player.name}
-                    placeholder="Player name"
-                />
+                <div class="flex items-center gap-2">
+                    <input
+                        class="input input-bordered input-sm w-full"
+                        type="text"
+                        bind:value={calculation.player.name}
+                        placeholder="Player name"
+                    />
+                    {#if isDirty(calculation)}
+                        <div class="badge badge-warning badge-sm shrink-0">
+                            Unsaved
+                        </div>
+                    {/if}
+                </div>
 
                 <ul
                     class="bg-base-100 rounded-box shadow-xs divide-y divide-base-300"
@@ -387,7 +440,7 @@
             <div class="flex gap-2">
                 <button
                     onclick={() => saveCalculation(calculation)}
-                    disabled={calculation.saving}
+                    disabled={calculation.saving || !isDirty(calculation)}
                     class="btn btn-primary btn-sm flex-1"
                 >
                     {calculation.saving ? "Saving..." : "Save"}