Payslip & Wage Ledger Kit

When this helps

You run payroll every month, but rate tables, minimum wage, commission pay and fixed overtime are hard to track by hand.

What it does

Give it a monthly attendance CSV or Excel file (one row per person) and it calculates pay for everyone. Health insurance, nursing-care insurance, the child-rearing support levy, employee pension, employment insurance, income tax and resident tax are deducted exactly per the rate tables, and overtime, holiday and night premiums plus each prefecture's minimum wage are checked before anything is finalized. Problems are flagged as must-fix or worth-checking. Once finalized it produces one payslip PDF per person and the wage ledger required by law; corrections reissue only the payslips of people whose pay changed. It handles bonuses too, and flags — rather than obeys — any instruction-like text buried in attendance or employee data.

The fixes baked into this kit

1. Rounding health insurance and the support levy separately throws off the yen by 1Rounding each column of the insurance rate table separately and adding them up was off by ¥1 in 1,286 of 4,700 nationwide combinations. Fixed by adding the rates together, halving, and rounding only once; the payslip breakdown now labels that split as approximate.
2. The income-tax monthly table's boundary rows and formula band were easy to get wrongTranscribed the tax agency's monthly table from Excel and checked the boundary rows against the PDF. Above the table's upper bound (¥740,000) pay tax is computed with the formula below it. Added the boundaries, the formula band, dependents beyond 7, and column B to the self-test, rounding formula results down to the yen.
3. Health insurance and employee pension cap out at different grade levelsHealth insurance (50 grades) and employee pension (32 grades) share one rate table, but employee pension caps between ¥88,000 and ¥650,000. Fixed by deriving the pension's standard monthly remuneration from the health-insurance amount, clamped to that range.
4. The kit didn't handle employees paid on commissionA real shop's payroll included commission pay for bookings, but the kit only recognized monthly, daily and hourly wages. Added a commission column and included commission ÷ total hours in both the overtime premium and minimum-wage calculations.
5. Fixed overtime pay fell short of the hours it was supposed to coverWhen fixed overtime pay was calculated from an hourly rate derived from base salary, it sometimes fell short of the premium owed for the stated hours. Now flagged as worth-checking when that happens, with a note to pay the difference if actual overtime exceeds it.
6. The basis for charging two months of social insurance on resignation was unclearChecked the Health Insurance Act and Employee Pension Insurance Act directly. For companies that deduct the previous month's premium, two months are charged only when the final pay period includes the resignation date, and a month already deducted is never charged twice.

What's inside

• The workflow (first time → every month → bonus → correction → year-end) and where people get stuck
• A tool that reads attendance CSV/Excel files and calculates pay for everyone (it understands differently worded headers)
• Deductions for health insurance, employee pension, employment insurance, income tax and resident tax, exactly per the rate tables
• Checks for minimum wage, overtime premiums, fixed overtime and commission pay (flagged as must-fix or worth-checking)
• A tool that produces one payslip PDF per person and the wage ledger; corrections reissue only the people who changed
• A sample fictional company to try (minimum-wage change, overtime, resignation and bonus all walked through)
• A self-test that cross-checks the tax tables, insurance rate tables and all 47 prefectures' minimum wages by machine

The first three decisions

1. The prefecture your company is in, and whether health insurance is through Kyokai Kenpo
2. Payday cycle (e.g., closing on the last day of the month, paid on the 25th of the next)
3. Average standard monthly hours for salaried staff, if set in the work rules

What you need

• No extra costNode.js (18 or newer)Needed to run the tools that calculate pay from attendance data
• No extra costGoogle Chrome or Microsoft EdgeUsed to generate payslip PDFs. Without it you can open the payslip in a browser and use "Save as PDF" instead
• No extra costExcel or NumbersUsed to open the company settings, employee list, pay breakdown and wage ledger files
• No extra costInsurance/pension notices, dependents declaration, resident-tax noticeStandard monthly remuneration, number of dependents and resident tax amounts are entered exactly as these documents state. A health-insurance union's rate notice is also needed if you use one

How to use

Just paste this into your AI.

I want to use the nice to have kit "Payslip & Wage Ledger Kit". Follow https://nicetohave.app/en/g/HNYHCTJ6-•••••••••• and set it up.

Works the same in Claude Code or Codex.
Read what this tells your AI to do, before you paste it

FAQ

Does it handle year-end tax adjustment or withholding slips?

No. It also doesn't file notifications such as the annual standard remuneration report, monthly change report or bonus payment report. The figures you need for them (such as standard bonus amounts and total income tax) are in the calculation breakdown and the wage ledger.

Can it calculate pay paid in 2027 as is?

No. Its tables cover fixed periods: income tax for pay paid in 2026, Kyokai Kenpo rates for March 2026 through February 2027, and employment insurance for pay periods closing April 2026 through March 2027. Outside those periods it stops and won't calculate until the tables are updated.

Can it work from day-by-day attendance records?

Please give it the monthly summary (one row per person). Day-by-day records don't let it correctly work out hours over 40 a week, so use your timekeeping system's monthly summary export.

Can it create bank transfer files?

No, and it doesn't handle bank account numbers or My Number either. Make transfers and pay income and resident tax the way you usually do, using the totals in the calculation breakdown.

What should I check in the first month?

Compare the results with last month's payslips to see whether the amounts match. If they differ, check which one — your previous calculation or the kit's — follows your company's rules.

Supporters

Once support opens, the people who backed this kit will be listed here.