Reading a 源泉徴収票 (withholding slip)

The 源泉徴収票 is the withholding slip your employer gives you in January. It summarizes the previous year's salary, tax withheld, and deductions already applied through 年末調整.

The six fields that matter most

1. 支払金額 — gross salary paid
2. 給与所得控除後の金額 — taxable income after the employment deduction
3. 所得控除の額の合計額 — total deductions applied by the employer
4. 源泉徴収税額 — income tax withheld
5. 社会保険料等の金額 — social-insurance premiums
6. 住宅借入金等特別控除の額 — housing-loan credit already applied

If you do file, the app usually starts from the gross-salary and withholding fields and recomputes the rest around them.