diff --git a/app/Http/Controllers/ProjectionController.php b/app/Http/Controllers/ProjectionController.php
index 050ab18..7a65daa 100644
--- a/app/Http/Controllers/ProjectionController.php
+++ b/app/Http/Controllers/ProjectionController.php
@@ -3,15 +3,20 @@
 namespace App\Http\Controllers;
 
 use App\Http\Requests\CalculateProjectionRequest;
+use App\Http\Requests\PreviewAllocationRequest;
 use App\Http\Resources\ProjectionResource;
+use App\Models\Bucket;
 use App\Models\Scenario;
+use App\Services\Projection\PipelineAllocationService;
 use App\Services\Projection\ProjectionGeneratorService;
 use Carbon\Carbon;
+use Illuminate\Http\JsonResponse;
 
 class ProjectionController extends Controller
 {
     public function __construct(
-        private readonly ProjectionGeneratorService $projectionGeneratorService
+        private readonly ProjectionGeneratorService $projectionGeneratorService,
+        private readonly PipelineAllocationService $pipelineAllocationService,
     ) {}
 
     public function calculate(CalculateProjectionRequest $request, Scenario $scenario): ProjectionResource
@@ -27,4 +32,45 @@ public function calculate(CalculateProjectionRequest $request, Scenario $scenari
 
         return new ProjectionResource($projections);
     }
+
+    public function preview(PreviewAllocationRequest $request, Scenario $scenario): JsonResponse
+    {
+        $amountInCents = (int) round($request->input('amount') * 100);
+
+        $draws = $this->pipelineAllocationService->allocateInflow($scenario, $amountInCents);
+
+        /** @var array<int, Bucket> $bucketLookup */
+        $bucketLookup = $scenario->buckets->keyBy('id')->all();
+
+        $allocations = $draws->map(function ($draw) use ($bucketLookup) {
+            $bucket = $bucketLookup[$draw->bucket_id];
+
+            return [
+                'bucket_id' => $bucket->uuid,
+                'bucket_name' => $bucket->name,
+                'bucket_type' => $bucket->type->value,
+                'allocated_amount' => $draw->amount_currency,
+                'remaining_capacity' => $this->remainingCapacity($bucket, $draw->amount_currency),
+            ];
+        })->values();
+
+        $totalAllocatedCents = $draws->sum('amount');
+
+        return response()->json([
+            'allocations' => $allocations,
+            'total_allocated' => round($totalAllocatedCents / 100, 2),
+            'unallocated' => round(($amountInCents - $totalAllocatedCents) / 100, 2),
+        ]);
+    }
+
+    private function remainingCapacity(Bucket $bucket, float $allocatedDollars): ?float
+    {
+        $effectiveCapacity = $bucket->getEffectiveCapacity();
+
+        if ($effectiveCapacity === PHP_FLOAT_MAX) {
+            return null;
+        }
+
+        return round(max(0, $effectiveCapacity - $allocatedDollars), 2);
+    }
 }
diff --git a/app/Http/Requests/PreviewAllocationRequest.php b/app/Http/Requests/PreviewAllocationRequest.php
new file mode 100644
index 0000000..42cbb93
--- /dev/null
+++ b/app/Http/Requests/PreviewAllocationRequest.php
@@ -0,0 +1,20 @@
+<?php
+
+namespace App\Http\Requests;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class PreviewAllocationRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'amount' => ['required', 'numeric', 'min:0.01'],
+        ];
+    }
+}
diff --git a/routes/web.php b/routes/web.php
index f6d296d..32ba796 100644
--- a/routes/web.php
+++ b/routes/web.php
@@ -38,6 +38,7 @@
 
 // Projection routes (no auth required for MVP)
 Route::post('/scenarios/{scenario}/projections/calculate', [ProjectionController::class, 'calculate'])->name('projections.calculate');
+Route::post('/scenarios/{scenario}/projections/preview', [ProjectionController::class, 'preview'])->name('projections.preview');
 
 // Auth dashboard (hidden for single-scenario MVP, re-enable later)
 // Route::middleware(['auth', 'verified'])->group(function () {