diff --git a/app/Models/Bucket.php b/app/Models/Bucket.php
index 216c9c2..b00697b 100644
--- a/app/Models/Bucket.php
+++ b/app/Models/Bucket.php
@@ -22,6 +22,7 @@
  * @property BucketAllocationTypeEnum $allocation_type
  * @property float $starting_amount
  * @property float $allocation_value
+ * @property float $buffer_multiplier
  *
  * @method static BucketFactory factory()
  */
@@ -38,6 +39,7 @@ class Bucket extends Model
         'sort_order',
         'allocation_type',
         'allocation_value',
+        'buffer_multiplier',
         'starting_amount',
     ];
 
@@ -46,6 +48,7 @@ class Bucket extends Model
         'priority' => 'integer',
         'sort_order' => 'integer',
         'allocation_value' => 'decimal:2',
+        'buffer_multiplier' => 'decimal:2',
         'starting_amount' => 'integer',
         'allocation_type' => BucketAllocationTypeEnum::class,
     ];
@@ -99,6 +102,21 @@ public function getCurrentBalance(): int
         return $this->starting_amount + $totalDraws - $totalOutflows;
     }
 
+    /**
+     * Get the effective capacity including buffer.
+     * Formula: allocation_value * (1 + buffer_multiplier)
+     */
+    public function getEffectiveCapacity(): float
+    {
+        if ($this->allocation_type !== BucketAllocationTypeEnum::FIXED_LIMIT) {
+            return PHP_FLOAT_MAX;
+        }
+
+        $base = (float) ($this->allocation_value ?? 0);
+
+        return round($base * (1 + (float) $this->buffer_multiplier), 2);
+    }
+
     /**
      * Check if the bucket can accept more money (for fixed_limit buckets).
      */
@@ -108,7 +126,7 @@ public function hasAvailableSpace(): bool
             return true;
         }
 
-        return $this->getCurrentBalance() < $this->allocation_value;
+        return $this->getCurrentBalance() < $this->getEffectiveCapacity();
     }
 
     /**
@@ -120,7 +138,7 @@ public function getAvailableSpace(): float
             return PHP_FLOAT_MAX;
         }
 
-        return max(0, $this->allocation_value - $this->getCurrentBalance());
+        return max(0, $this->getEffectiveCapacity() - $this->getCurrentBalance());
     }
 
     /**
diff --git a/database/factories/BucketFactory.php b/database/factories/BucketFactory.php
index f7dada7..22d31bb 100644
--- a/database/factories/BucketFactory.php
+++ b/database/factories/BucketFactory.php
@@ -46,6 +46,7 @@ public function definition(): array
             'sort_order' => $this->faker->numberBetween(0, 10),
             'allocation_type' => $allocationType,
             'allocation_value' => $this->getAllocationValueForType($allocationType),
+            'buffer_multiplier' => 0,
             'starting_amount' => $this->faker->numberBetween(0, 100000), // $0 to $1000 in cents
         ];
     }
@@ -119,6 +120,16 @@ public function overflow(): Factory
         ]);
     }
 
+    /**
+     * Create a bucket with a buffer multiplier.
+     */
+    public function withBuffer(float $multiplier): Factory
+    {
+        return $this->state([
+            'buffer_multiplier' => $multiplier,
+        ]);
+    }
+
     /**
      * Create default buckets set (Monthly Expenses, Emergency Fund, Overflow).
      */
diff --git a/tests/Unit/BucketTest.php b/tests/Unit/BucketTest.php
index da29f3b..6dbf7f7 100644
--- a/tests/Unit/BucketTest.php
+++ b/tests/Unit/BucketTest.php
@@ -79,4 +79,98 @@ public function test_current_balance_without_starting_amount_defaults_to_zero()
         // starting_amount (0) + draws (30000) - outflows (10000) = 20000
         $this->assertEquals(20000, $bucket->getCurrentBalance());
     }
+
+    public function test_effective_capacity_with_zero_buffer_equals_allocation_value(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'buffer_multiplier' => 0,
+        ]);
+
+        $this->assertEquals(50000.0, $bucket->getEffectiveCapacity());
+    }
+
+    public function test_effective_capacity_with_full_buffer_doubles_capacity(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        $this->assertEquals(100000.0, $bucket->getEffectiveCapacity());
+    }
+
+    public function test_effective_capacity_with_half_buffer(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'buffer_multiplier' => 0.5,
+        ]);
+
+        $this->assertEquals(75000.0, $bucket->getEffectiveCapacity());
+    }
+
+    public function test_effective_capacity_for_percentage_returns_php_float_max(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->percentage(25)->create([
+            'scenario_id' => $scenario->id,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        $this->assertEquals(PHP_FLOAT_MAX, $bucket->getEffectiveCapacity());
+    }
+
+    public function test_effective_capacity_for_unlimited_returns_php_float_max(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->unlimited()->create([
+            'scenario_id' => $scenario->id,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        $this->assertEquals(PHP_FLOAT_MAX, $bucket->getEffectiveCapacity());
+    }
+
+    public function test_has_available_space_uses_effective_capacity(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'starting_amount' => 50000,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        // Balance is 50000, effective capacity is 100000 — still has space
+        $this->assertTrue($bucket->hasAvailableSpace());
+    }
+
+    public function test_has_available_space_false_when_at_effective_capacity(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'starting_amount' => 100000,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        // Balance is 100000, effective capacity is 100000 — no space
+        $this->assertFalse($bucket->hasAvailableSpace());
+    }
+
+    public function test_get_available_space_uses_effective_capacity(): void
+    {
+        $scenario = Scenario::factory()->create();
+        $bucket = Bucket::factory()->fixedLimit(50000)->create([
+            'scenario_id' => $scenario->id,
+            'starting_amount' => 30000,
+            'buffer_multiplier' => 1.0,
+        ]);
+
+        // Effective capacity 100000 - balance 30000 = 70000 available
+        $this->assertEquals(70000.0, $bucket->getAvailableSpace());
+    }
 }