年末調整の仕組み — 会社員のための税精算
年末調整とは、給与を支払う会社（源泉徴収義務者）が、従業員の1年間の給与と源泉徴収税額を精算する制度です。毎月の給与から概算で源泉徴収されている所得税を、年末に正しい年税額と比較し、過不足を精算します。多くの会社員は年末調整だけで納税が完結し、確定申告は不要です。
Year-end adjustment is the system by which the salary-paying company (the withholding obligor) reconciles each employee's annual salary and withheld tax. The income tax withheld monthly from salary based on an estimate is compared at year-end with the correct annual tax amount, and any excess or shortage is settled. For most company employees, taxation is completed solely through year-end adjustment, with no need for a final tax return.
年末調整の対象者
年末調整の対象は、その年の12月31日時点で勤務しており、「給与所得者の扶養控除等（異動）申告書」を提出している従業員です。年の途中で退職した人でも、12月に支払う給与の計算までに退職した場合は一定の条件で対象となります。ただし、給与年収が2,000万円を超える人や、災害減免法により源泉徴収の猶予を受けている人は年末調整の対象外となり、確定申告が必要です。
Year-end adjustment applies to employees who are employed as of December 31 and have submitted the "Declaration Concerning Dependent Deductions etc. of Salary Earners (Change Notification)." It also applies in certain cases to those who retired mid-year if they retired before December's salary calculation. However, those whose annual salary exceeds 20 million yen and those who have received a withholding deferment under the Disaster Reduction Act are excluded and must file a final return.
確定申告との違い
年末調整と確定申告の最大の違いは「手続きを誰が行うか」です。年末調整は勤務先（会社）が従業員に代わって税額を計算・精算します。従業員は必要な申告書と控除証明書（保険会社からの証明書等）を勤務先に提出するだけです。一方、確定申告は本人が税務署に直接申告します。
The biggest difference between year-end adjustment and the final tax return is "who performs the procedure." In year-end adjustment, the employer calculates and settles tax on behalf of the employee. The employee only needs to submit the required declaration forms and deduction certificates (such as those from insurance companies) to the employer. In contrast, the final tax return is filed directly by the individual at the tax office.
提出必要な3つの申告書
従業員が勤務先に提出する年末調整関連書類は原則3種類です。①給与所得者の扶養控除等（異動）申告書：扶養家族の氏名・生年月日・マイナンバー等を記載。翌年分を年末に提出し、当年分は年初に既に提出済みが一般的。
Employees typically submit three types of year-end adjustment documents to their employer. (1) Declaration Concerning Dependent Deductions etc. of Salary Earners (Change Notification): records dependent family members' names, dates of birth, and My Number. The form for the next year is submitted at year-end, while the current year's form has typically already been submitted at the beginning of the year.
②給与所得者の保険料控除申告書：生命保険料・地震保険料・社会保険料（国民年金など給与天引きされていない分）・小規模企業共済等掛金（iDeCoを含む）の控除を申請。各保険会社から10月〜11月に送付される「控除証明書」を添付します。
(2) Insurance Premium Deduction Declaration for Salary Earners: applies for deductions of life insurance, earthquake insurance, social insurance (such as National Pension portions not deducted from salary), and small enterprise mutual aid premiums (including iDeCo). Attach the "deduction certificates" mailed by each insurance company in October-November.
③給与所得者の基礎控除申告書 兼 給与所得者の配偶者控除等申告書 兼 所得金額調整控除申告書：基礎控除（原則48万円、本人所得2,400万円超は逓減）、配偶者控除・配偶者特別控除（配偶者の年間合計所得が133万円以下）、23歳未満の扶養親族等に該当する場合の所得金額調整控除を一括申告する書類です。
(3) Combined form for Basic Deduction + Spousal Deduction + Income Adjustment Deduction Declaration of Salary Earners: a single document declaring the basic deduction (in principle 480,000 yen, gradually decreased for personal income exceeding 24 million yen), spousal deduction / special spousal deduction (when spouse's annual total income is 1.33 million yen or less), and income adjustment deduction when there are dependent relatives under 23 years old, etc.
年末調整で適用できる控除
年末調整で自動適用される主な控除は次のとおりです。①基礎控除（最大48万円）、②給与所得控除（収入に応じて自動計算・最低55万円）、③扶養控除（一般38万円・特定63万円・老人48万円・同居老親58万円）、④配偶者控除・配偶者特別控除、⑤障害者控除・寡婦控除・ひとり親控除・勤労学生控除、⑥社会保険料控除（健康保険・厚生年金・雇用保険）、⑦小規模企業共済等掛金控除（iDeCo含む）、⑧生命保険料控除・地震保険料控除、⑨住宅借入金等特別控除（2年目以降のみ）。
Deductions automatically applied via year-end adjustment include: (1) basic deduction (max 480,000 yen), (2) employment income deduction (auto-calculated by income, min 550,000 yen), (3) dependent deduction (general 380K, specified 630K, elderly 480K, cohabiting elderly parent 580K yen), (4) spousal deduction / special spousal deduction, (5) deductions for disabled persons, widows, single parents, working students, (6) social insurance premium deduction (health insurance, employees' pension, employment insurance), (7) small enterprise mutual aid premium deduction (including iDeCo), (8) life insurance and earthquake insurance premium deductions, (9) special deduction for housing loans (year 2 onward only).
年末調整では適用できない控除
次の控除は年末調整では適用されず、本人が確定申告を行う必要があります。①医療費控除（年間10万円超の医療費）、②寄附金控除（ふるさと納税をワンストップ特例で処理しなかった場合・5自治体超に寄附した場合）、③雑損控除（災害・盗難による損失）、④住宅借入金等特別控除の初年度（2年目以降は年末調整で可能）です。
The following deductions are not applied via year-end adjustment, requiring the individual to file a final tax return: (1) medical expense deduction (annual medical costs over 100,000 yen), (2) donation deduction (when furusato nozei is not handled via the One-Stop exception, or donations to more than 5 municipalities), (3) casualty loss deduction (losses from disaster or theft), (4) housing loan special deduction in the first year (year 2 onward can be done via year-end adjustment).
精算結果：還付か追加徴収か
年末調整の計算結果、源泉徴収税額が年税額より多い場合は還付（戻り）、少ない場合は追加徴収（追徴）が行われます。多くの会社員は還付になりやすく、12月または翌年1月の給与で還付金が支給されるのが一般的です。年末調整後、従業員には「源泉徴収票」が交付され、これが年間所得と納付税額の公式証明となります。
Based on the year-end adjustment calculation, if the withheld tax exceeds the annual tax amount, a refund is issued; if it is less, additional collection occurs. Many company employees end up with refunds, typically paid out via the December or following January salary. After year-end adjustment, employees receive a "Withholding Tax Certificate" (gensen choshu hyo), which serves as official proof of annual income and tax paid.