Employer not withholding taxes

All of my previous employers withheld taxes.
I think it's easier because I don't have to file taxes in Japan.
What money I don't get and is withheld I won't miss.

I was offered a position, but the employer doesn't withhold taxes.
Because technically I am "self-employed".
How much money should I put aside for when I file taxes and owe money?
I will be making 320,000 a month.

The short answer is: Go to your local tax office while they're still offering free advise from professional tax accountants for the tax paying season. They will tell you everything.

The longer answer is that it totally depends on expenses you will be paying per year, what kind of deductions you will be having depending on how you manage your pensions and health insurance, etc. etc. etc., which has a lot to do with what kind of a job you're specifically going to do for the year, including your other jobs that you are free to do.

Because taxes don't work "per month". They work "per fiscal year".

In any case, a self-employer earning 320,000 a month isn't at all the same thing as a salary-man earning 320,000 a month, because typically self-employers don't get any bonuses or welfare programs or paid holidays or transportation fees unless your contract mentions otherwise.

It is pretty easy to work out. Multiply you monthly income by 12 for you yearly amount. Then check the Japan taxation website for how much you should pay on that amount. Keep that amount aside when it comes time to do your taxes so you are ready to pay the bill.

If the employer isn`t doing the taxes - I am guessing that they are not paying their half of the health insurance and pension - so you pay both halves, and this will reduce your taxable income significantly - leaving less spendable money with you, but somewhat reduced taxes too as you take a deduction for them.

And.... keep all of your reciepts for anything medical, including over the counter meds from a store. Keep track of transportation costs. These also reduce your taxable income.

You can also go to your city tax office -- probably at your City Hall -- for help, and where I live, that's often the better choice. It's less crowded than the national tax office, and the people are more knowledgeable and will help you fill out the forms.

If you think you'll owe tax next year, they can send you a yotei-zei reminder three times during the year so you're not hit with a big tax bill later and with possible late penalties.

Also, what's your nationality? If you are USA, definitely try to get your employer to give you a year-end slip showing withholding of taxes. Otherwise, if you're treated as self-employed, you will have to file a US Schedule C and Form SE, and pay and additional 15.3% in US Social Security tax, even if you can exclude the income on a Form 2555!

generally speaking,
if it is a salary, the employer MUST withhold income tax. it means the employer violates income tax law.
( I don't believe that the employer did not withhold the tax, because the penalty for the employer is very high.)
if it is not a salary, you mention you are "self-employed". if so, what kind of residential status do you have ?

about income tax,
if you are paid as a salary, you can have automatic deduction,給与所得控除.
annual income : 320000yen x 12=3840000 yen.　the deduction is 1332000 yen (if you work in a whole year).
if not paid as a salary (self-employed), you can't have that deduction. you have to file all expenses.

if you received 給与所得の源泉徴収票, money was paid as a salary.
if your 2017's income of the present company was less than 1080000 yen, income tax might be shown as zero.
but, you have to combine the two (or more) 源泉徴収票 of the previous and present companies and re-calculate the income tax.

I'd say go to your tax office soon with a copy of whatever you have (a pay slip, your bank book, etc.) and ask for advice.

And, as mentioned above, if you're an American citizen, the "self-employed" status is bad for you because you're going to have to pay 15% of that self-employed income, after expenses, in American Social Security tax.

I'm from the U.S. and I ran into that! Having no taxes withheld and being self employed means I need to keep records for everything, including my expenses, and I have to pay the IRS a good chunk of my self employed income every year for social security. I think it is about 15 percent, as someone said above. It was a pain so I finally ended up using a tax preparer, and that costs me money too. AND I also have to pay U.S. estimated taxes every year to avoid being hit with a penalty by the IRS for underpayment.

What's your nationality? If it's U.S., really really really try to get the company to take out Japanese tax and give you a statement at the end of the year showing the amount of tax you had withheld so you are not under the self employed category.