Vehicle Tax Proration Calculator (Japan)
Estimate the prorated Japanese automobile tax when you register a regular or compact car partway through the fiscal year, or deregister (scrap) one. Enter the displacement, fuel type, and registration date to see the estimated amount due or refunded.
What Is Vehicle Tax Proration?
Japan's vehicle tax (jidōsha-zei) is billed as a single lump sum each year to whoever owns the car as of April 1. When a car is newly registered or deregistered partway through the fiscal year, though, the amount is prorated so it reflects only the months the car was actually owned. Register a new or used car mid-year and you're taxed starting the month after registration; deregister one to scrap it and you typically get a refund for the months remaining after you gave it up.
This tool estimates that prorated amount, or the refund, from just three inputs: engine displacement, fuel type, and the registration (or deregistration) date. The annual tax itself is set by displacement and fuel type — gasoline/LPG, diesel, or electric — and can rise sharply once a gasoline or diesel car passes a certain age, under a rule known as the aged-vehicle surcharge. Kei cars are taxed under a separate, non-prorated system, so this calculator covers only regular and compact passenger cars.
Sources used in this calculation
Statutory figures such as tax and insurance rates come from the public bodies listed below. They change when the law is revised, so please also check the primary source before relying on the result for an important decision.
- Monthly proration of automobile tax and its rounding unit — Ministry of Internal Affairs and Communications (総務省) Effective from 2019-10 ／ Last checked 2026-09-21
How to Use the Vehicle Tax Proration Calculator
- Choose the procedure Select whether you're working through a "new registration (purchase)" or a "deregistration (scrapping)".
- Enter the engine displacement Type in the displacement (in cc) shown on your vehicle inspection certificate.
- Select the fuel type Choose gasoline/LPG, diesel, or electric vehicle (EV) — this determines the annual tax rate that applies.
- Enter the registration date(s) For a new registration, enter the registration date. For a deregistration, enter both the first registration date and the deregistration date.
- Review the estimated prorated tax The result shows the prorated amount alongside the taxed months, annual tax, and which rate (old or new) applies.
Tips for getting more out of it
- The first registration date appears on your vehicle inspection certificate (shaken-sho). When scrapping a used car, enter the date it was first registered by its original owner.
- New registrations are taxed from the month after registration, while deregistrations are taxed from April through the month of deregistration — the counting rule shifts by one month between the two.
- Kei car tax has no proration system and is charged in full to whoever owns the car as of April 1, so this tool only covers regular and compact cars.
- Registering a car in March means the next fiscal year already starts in April, so the taxed months for that fiscal year come out to zero.
When This Calculator Comes in Handy
Budgeting before registering a temporarily deregistered used car
When a used car that has been temporarily deregistered is registered again, the first-year vehicle tax is charged monthly from the registration month. Knowing the amount in advance helps you estimate the purchase costs. Buying a car that is already registered and simply transferring the name does not trigger a prorated charge.
Checking a refund before scrapping a car
If you're giving up a car partway through the fiscal year, get a quick estimate of how much you should expect back as a refund.
Deciding whether to shift the registration date
Compare how registering at the end versus the start of a month changes the number of taxed months — useful when negotiating a delivery date.
Double-checking a dealer's quote
Verify for yourself whether the prorated vehicle tax a dealership included in its quote looks like a reasonable figure.
Vehicle Tax Glossary
- Vehicle tax (jidōsha-zei)
- A prefectural tax charged annually to owners of regular and compact passenger cars, based on engine displacement. It was renamed "shubetsu-wari" in the 2019 tax reform, but reverted to plain "jidōsha-zei" on 1 April 2026 when the environmental performance levy was abolished.
- Proration (tsukiwari)
- The practice of calculating tax by the month, rather than the day, whenever a car is newly registered or deregistered partway through the fiscal year, so the bill reflects only the period of actual ownership.
- Aged-vehicle surcharge (keinen-jūka)
- A higher tax rate applied once a gasoline/LPG car passes 13 years, or a diesel car passes 11 years, since first registration. It's meant to encourage replacing older, less environmentally friendly cars with newer ones.
- New registration / deregistration
- New registration is the procedure for registering a new car or a temporarily deregistered used car; deregistration removes a car from the register when it is scrapped or taken off the road. These are the start and end points of the monthly proration. A change of owner (transfer registration) or moving to another prefecture does not trigger any proration.
- Environmental performance surcharge (kankyō seinō-wari)
- A tax formerly charged at acquisition according to fuel efficiency. It was abolished on March 31, 2026, so acquisitions on or after April 1, 2026 are not taxed. It was a separate tax from the vehicle tax that this tool prorates.
- Old rate / new rate
- Cars first registered on or after October 2019 are taxed at a reduced new rate; cars registered before that date remain on the older, higher rate.
Frequently asked questions
Side Note — Why registration and deregistration count months differently
Japan's vehicle tax proration system exists to reconcile the annual tax, which is fixed as of April 1, with how long a car was actually owned. Without proration, someone buying a new car partway through the year would owe a full year's tax despite driving it for only part of that time, while someone scrapping a car early in the year would keep paying tax for months they no longer owned it. Prorating the amount by month is a practical way to reduce that mismatch.
It is easy to overlook that new registrations and deregistrations count the registration/deregistration month itself differently. A new registration is not taxed for its own month — counting starts the following month. A deregistration, on the other hand, includes its own month as part of the taxed period for that fiscal year, with the refund beginning only the month after. The same calendar month is counted from opposite ends depending on whether you are acquiring or giving up the car.
Used car dealers sometimes work this calculation backward, advising buyers that registering early in the month is slightly better since the following month is where taxation actually begins. In practice the difference usually amounts to only a few thousand yen, but if you are buying or selling near the end of the fiscal year, shifting the registration date by even a day can change the number of taxed months — worth a quick check with the dealer.