修正

Co-authored-by: Copilot <copilot@github.com>

backend/app/payroll/calculation/service.py

@@ -1,7 +1,7 @@
 """
 給与計算サービス (Payroll Calculation Service)
 """
-from decimal import Decimal
+from decimal import Decimal, ROUND_HALF_UP
 from datetime import date
 from typing import Dict, Any
 from ...core.database import get_connection
@@ -58,8 +58,10 @@ class PayrollCalculationService:
         """保険料率を取得（年度がない場合は前年度を参照）"""
         with get_connection() as conn:
             with conn.cursor() as cur:
-                # rate_yearで年度を判定
-                target_year = target_date.year
+                # 翌月払いのため、新年度料率は5月支払分（4月分）から適用
+                # rate_year=XXXX は XXXX年5月支払〜(XXXX+1)年4月支払に適用
+                # 1〜4月支払は前年度（year-1）の料率を使用
+                target_year = target_date.year if target_date.month >= 5 else target_date.year - 1
                 cur.execute(
                     """
                     SELECT * FROM insurance_rates 
@@ -300,7 +302,7 @@ class PayrollCalculationService:
                 # まず指定年度の標準報酬月額表を検索
                 cur.execute(
                     """
-                    SELECT monthly_amount, child_support
+                    SELECT monthly_amount
                     FROM standard_remuneration 
                     WHERE rate_year = %s
                     AND salary_from <= %s
@@ -318,7 +320,7 @@ class PayrollCalculationService:
                         previous_year = target_year - year_offset
                         cur.execute(
                             """
-                            SELECT monthly_amount, child_support
+                            SELECT monthly_amount
                             FROM standard_remuneration 
                             WHERE rate_year = %s
                             AND salary_from <= %s
@@ -334,11 +336,9 @@ class PayrollCalculationService:
                 
                 if result:
                     standard_monthly_salary = Decimal(str(result["monthly_amount"]))
-                    child_support_full = Decimal(str(result["child_support"])) if result["child_support"] is not None else Decimal("0")
-                    print(f"[DEBUG] 標準報酬月額表検索: 総支給額={total_payment} → 標準報酬月額={standard_monthly_salary}, 子育て支援金全額={child_support_full}")
+                    print(f"[DEBUG] 標準報酬月額表検索: 総支給額={total_payment} → 標準報酬月額={standard_monthly_salary}")
                 else:
                     print(f"[DEBUG] 標準報酬月額表検索: 該当等級なし（総支給額={total_payment}）")
-                    child_support_full = Decimal("0")
 
         
         # 社会保険料上限を取得
@@ -381,7 +381,7 @@ class PayrollCalculationService:
         if health_insurance_rate:
             health_insurance = (
                 health_standard_salary * Decimal(str(health_insurance_rate["employee_rate"]))
-            ).quantize(Decimal("0.01"))
+            ).quantize(Decimal("1"), rounding=ROUND_HALF_UP)
         elif calc_social_insurance:
             errors.append(f"健康保険料率が見つかりません（年度: {payment_date.year}）")
         
@@ -392,7 +392,7 @@ class PayrollCalculationService:
             if care_insurance_rate:
                 care_insurance = (
                     health_standard_salary * Decimal(str(care_insurance_rate["employee_rate"]))
-                ).quantize(Decimal("0.01"))
+                ).quantize(Decimal("1"), rounding=ROUND_HALF_UP)
                 print(f"[DEBUG] 介護保険計算: {health_standard_salary} × {care_insurance_rate['employee_rate']}% = {care_insurance}")
             else:
                 errors.append(f"介護保険料率が見つかりません（年度: {payment_date.year}）") if calc_social_insurance else None
@@ -403,7 +403,7 @@ class PayrollCalculationService:
         if pension_insurance_rate:
             pension_insurance = (
                 pension_standard_salary * Decimal(str(pension_insurance_rate["employee_rate"]))
-            ).quantize(Decimal("0.01"))
+            ).quantize(Decimal("1"), rounding=ROUND_HALF_UP)
             print(f"[DEBUG] 厚生年金計算: {pension_standard_salary} × {pension_insurance_rate['employee_rate']}% = {pension_insurance}")
         elif calc_social_insurance:
             errors.append(f"厚生年金保険料率が見つかりません（年度: {payment_date.year}）")
@@ -412,14 +412,19 @@ class PayrollCalculationService:
         employment_insurance_rate = PayrollCalculationService.get_insurance_rate("雇用保険", payment_date)
         employment_insurance = Decimal("0")
         
-        # 子ども・子育て支援金（令和8年4月分以降のみ適用）
+        # 子ども・子育て支援金（令和8年4月分＝5月納付分以降のみ適用）
+        # 翌月払いのため、payroll_month=5（5月支払）が4月分保険料の初回控除月
         child_support = Decimal("0")
         is_child_support_applicable = (
-            (payroll_year == 2026 and payroll_month >= 4) or payroll_year >= 2027
+            (payroll_year == 2026 and payroll_month >= 5) or payroll_year >= 2027
         )
         if is_child_support_applicable and calc_social_insurance:
-            child_support = (child_support_full / Decimal("2")).quantize(Decimal("0.01"))
-            print(f"[DEBUG] 子育て支援金: 全額={child_support_full} → 折半額（従業員負担）={child_support}")
+            child_support_rate = PayrollCalculationService.get_insurance_rate("子ども・子育て支援金", payment_date)
+            if child_support_rate:
+                child_support = (
+                    standard_monthly_salary * Decimal(str(child_support_rate["employee_rate"]))
+                ).quantize(Decimal("1"), rounding=ROUND_HALF_UP)
+                print(f"[DEBUG] 子育て支援金: 標準報酬月額={standard_monthly_salary} × 料率={child_support_rate['employee_rate']} = {child_support}")
 
         # 雇用保険加入対象かどうか確認
         is_employment_insurance_eligible = salary_setting.get("employment_insurance_eligible", True) if salary_setting else True
@@ -427,7 +432,7 @@ class PayrollCalculationService:
         if is_employment_insurance_eligible and employment_insurance_rate:
             employment_insurance = (
                 total_payment * Decimal(str(employment_insurance_rate["employee_rate"]))
-            ).quantize(Decimal("0.01"))
+            ).quantize(Decimal("1"), rounding=ROUND_HALF_UP)
         elif not is_employment_insurance_eligible:
             print(f"[DEBUG] この従業員は雇用保険非対象です")
         elif not employment_insurance_rate and calc_social_insurance: