diff --git a/card-settlement-migration/src/test/java/com/bais/card/settlement/SettlementCalculatorTest.java b/card-settlement-migration/src/test/java/com/bais/card/settlement/SettlementCalculatorTest.java
new file mode 100644
index 0000000..75b58a6
--- /dev/null
+++ b/card-settlement-migration/src/test/java/com/bais/card/settlement/SettlementCalculatorTest.java
@@ -0,0 +1,193 @@
+package com.bais.card.settlement;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import java.math.BigDecimal;
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * SettlementCalculator 단위 테스트
+ * 불변식 검증: BRAND_SETTLEMENT_*, IRD_*, ISSUER_FEE_*, AMOUNT_*, ROUNDING_MODE
+ */
+@DisplayName("SettlementCalculator 불변식 테스트")
+class SettlementCalculatorTest {
+
+    private SettlementCalculator calculator;
+
+    @BeforeEach
+    void setUp() {
+        calculator = new SettlementCalculator();
+    }
+
+    @Nested
+    @DisplayName("브랜드 정산 불변식 테스트")
+    class BrandSettlementTests {
+
+        @Test
+        @DisplayName("BRAND_SETTLEMENT_FORMULA: 정산금 = 승인금액 - 취소금액 - 수수료")
+        void testSettlementFormula() {
+            BigDecimal approved = new BigDecimal("100000");
+            BigDecimal cancelled = new BigDecimal("10000");
+            BigDecimal rate = new BigDecimal("0.02");
+
+            SettlementCalculator.BrandSettlementResult result = 
+                calculator.calculateBrandSettlement(approved, cancelled, rate);
+
+            assertEquals(new BigDecimal("2000.00"), result.getCommission());
+            assertEquals(new BigDecimal("88000.00"), result.getSettlementAmount());
+        }
+
+        @Test
+        @DisplayName("BRAND_SETTLEMENT_NON_NEGATIVE: 정산금은 0 이상")
+        void testSettlementNonNegative() {
+            SettlementCalculator.BrandSettlementResult result = 
+                calculator.calculateBrandSettlement(
+                    new BigDecimal("10000"), new BigDecimal("20000"), new BigDecimal("0.02"));
+            assertEquals(BigDecimal.ZERO.setScale(2), result.getSettlementAmount());
+        }
+
+        @Test
+        @DisplayName("BRAND_COMMISSION_RATE_DEFAULT: 미지정 시 0.02")
+        void testDefaultCommissionRate() {
+            SettlementCalculator.BrandSettlementResult result = 
+                calculator.calculateBrandSettlement(
+                    new BigDecimal("100000"), BigDecimal.ZERO, null);
+            assertEquals(new BigDecimal("0.02"), result.getCommissionRate());
+        }
+    }
+
+    @Nested
+    @DisplayName("IRD 불변식 테스트")
+    class IrdTests {
+
+        @Test
+        @DisplayName("IRD_FORMULA: IRD = 승인금액 * IRD율")
+        void testIrdFormula() {
+            BigDecimal ird = calculator.calculateIRD(
+                new BigDecimal("100000"), new BigDecimal("0.015"));
+            assertEquals(new BigDecimal("1500.00"), ird);
+        }
+
+        @Test
+        @DisplayName("IRD_RATE_DEFAULT: 미지정 시 0.015")
+        void testDefaultIrdRate() {
+            BigDecimal ird = calculator.calculateIRD(new BigDecimal("100000"), null);
+            assertEquals(new BigDecimal("1500.00"), ird);
+        }
+
+        @Test
+        @DisplayName("IRD_NON_NEGATIVE: IRD는 0 이상")
+        void testIrdNonNegative() {
+            BigDecimal ird = calculator.calculateIRD(
+                new BigDecimal("100000"), new BigDecimal("-0.015"));
+            assertTrue(ird.compareTo(BigDecimal.ZERO) >= 0);
+        }
+    }
+
+    @Nested
+    @DisplayName("발급사 수수료 불변식 테스트")
+    class IssuerFeeTests {
+
+        @Test
+        @DisplayName("ISSUER_FEE_FORMULA: 발급사 수수료 = IRD * 발급사 수수료율")
+        void testIssuerFeeFormula() {
+            BigDecimal fee = calculator.calculateIssuerFee(
+                new BigDecimal("1500.00"), new BigDecimal("0.005"));
+            assertEquals(new BigDecimal("7.50"), fee);
+        }
+
+        @Test
+        @DisplayName("ISSUER_FEE_RATE_DEFAULT: 미지정 시 0.005")
+        void testDefaultIssuerFeeRate() {
+            BigDecimal fee = calculator.calculateIssuerFee(new BigDecimal("1500.00"), null);
+            assertEquals(new BigDecimal("7.50"), fee);
+        }
+
+        @Test
+        @DisplayName("ISSUER_SETTLEMENT_FORMULA: 발급사 정산금 = IRD - 발급사 수수료")
+        void testIssuerSettlementFormula() {
+            SettlementCalculator.IssuerSettlementResult result = 
+                calculator.calculateIssuerSettlement(
+                    new BigDecimal("1500.00"), new BigDecimal("0.005"));
+            assertEquals(new BigDecimal("7.50"), result.getIssuerFee());
+            assertEquals(new BigDecimal("1492.50"), result.getIssuerSettlement());
+        }
+    }
+
+    @Nested
+    @DisplayName("공통 금액 검증 불변식 테스트")
+    class AmountValidationTests {
+
+        @Test
+        @DisplayName("AMOUNT_NOT_NULL: null 시 IllegalArgumentException")
+        void testNullAmount() {
+            assertThrows(IllegalArgumentException.class, () -> 
+                calculator.calculateBrandSettlement(null, BigDecimal.ZERO, new BigDecimal("0.02")));
+        }
+
+        @Test
+        @DisplayName("AMOUNT_NON_NEGATIVE: 음수 시 IllegalArgumentException")
+        void testNegativeAmount() {
+            assertThrows(IllegalArgumentException.class, () -> 
+                calculator.calculateBrandSettlement(
+                    new BigDecimal("-100000"), BigDecimal.ZERO, new BigDecimal("0.02")));
+        }
+
+        @Test
+        @DisplayName("AMOUNT_MAX_LIMIT: 최대 한도 초과 시 IllegalArgumentException")
+        void testAmountExceedsMaxLimit() {
+            BigDecimal exceedsMax = new BigDecimal("999999999999.99").add(BigDecimal.ONE);
+            assertThrows(IllegalArgumentException.class, () -> 
+                calculator.calculateBrandSettlement(
+                    exceedsMax, BigDecimal.ZERO, new BigDecimal("0.02")));
+        }
+    }
+
+    @Nested
+    @DisplayName("금액 정밀도 불변식 테스트")
+    class PrecisionTests {
+
+        @Test
+        @DisplayName("AMOUNT_SCALE: 소수점 2자리")
+        void testAmountScale() {
+            SettlementCalculator.BrandSettlementResult result = 
+                calculator.calculateBrandSettlement(
+                    new BigDecimal("100000"), BigDecimal.ZERO, new BigDecimal("0.023456"));
+            assertEquals(2, result.getCommission().scale());
+            assertEquals(new BigDecimal("2345.60"), result.getCommission());
+        }
+
+        @Test
+        @DisplayName("ROUNDING_MODE: HALF_UP 반올림")
+        void testHalfUpRounding() {
+            SettlementCalculator.BrandSettlementResult result = 
+                calculator.calculateBrandSettlement(
+                    new BigDecimal("100000"), BigDecimal.ZERO, new BigDecimal("0.023455"));
+            assertEquals(new BigDecimal("2345.50"), result.getCommission());
+        }
+    }
+
+    @Nested
+    @DisplayName("전체 정산 흐름 테스트")
+    class FullSettlementTests {
+
+        @Test
+        @DisplayName("전체 정산 계산 통합 테스트")
+        void testFullSettlement() {
+            SettlementCalculator.FullSettlementResult result = 
+                calculator.calculateFullSettlement(
+                    new BigDecimal("100000"),
+                    new BigDecimal("10000"),
+                    new BigDecimal("0.02"),
+                    new BigDecimal("0.015"),
+                    new BigDecimal("0.005"));
+
+            assertNotNull(result.getBrandSettlement());
+            assertNotNull(result.getIrd());
+            assertNotNull(result.getIssuerSettlement());
+            assertEquals(new BigDecimal("1500.00"), result.getIrd());
+        }
+    }
+}