diff --git a/lib/rex/order.rb b/lib/rex/order.rb
index acf1092..8d6882e 100644
--- a/lib/rex/order.rb
+++ b/lib/rex/order.rb
@@ -25,5 +25,8 @@ module Rex
       @next_order = nil
     end
 
+    def filled?
+      remaining_amount == 0
+    end
   end
 end
diff --git a/spec/order_spec.rb b/spec/order_spec.rb
new file mode 100644
index 0000000..cdb1aa2
--- /dev/null
+++ b/spec/order_spec.rb
@@ -0,0 +1,27 @@
+# frozen_string_literal: true
+
+RSpec.describe Rex::Order do
+  describe "#filled?" do
+    let(:order) do
+      instance = described_class.new(
+        amount: 100
+      )
+      instance.remaining_amount = remaining_amount
+      instance
+    end
+
+    subject { order.filled? }
+
+    context "when remaining amount is not zero" do
+      let(:remaining_amount) { 50 }
+
+      it { is_expected.to be(false) }
+    end
+
+    context "when remaining amount is zero" do
+      let(:remaining_amount) { 0 }
+
+      it { is_expected.to be(true) }
+    end
+  end
+end