Taxation of Japanese Social Security in US

Hello, my wife is a green card holder and she lives in the US. She is about to retire, she will receive both, Japanese retirement and US Social security benefits, she worked in both countries. I was wondering if she needs to report her Japanese pension on form 1040 and if any portion her Japanese retirement pension is taxable in the US.

Thank you,

Pete

https://www.irs.gov/Businesses/The-Taxation-of-Foreign-Pension-and-Ann...

When she left Japan, has she "removed" herself from the resident register ("juminhyo") saying that she has moved out, thus stopped paying into the Japanese pension, system I assume?

I believe there is a way to "add" the years of contribution (or credits) into the Japanese system and the US system together, and receive the calculated total in the US.

...."When she left Japan, has she "removed" herself from the resident register ("juminhyo") saying that she has moved out, thus stopped paying into the Japanese pension, system I assume?
I believe there is a way to "add" the years of contribution (or credits) into the Japanese system and the US system together, and receive the calculated total in the US."....
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She has enough credits to receive both, Japanese and US Social security benefits. She worked in Japan for 20 + years (US 18 years) and until now she has been contributing to her employer setup pension/savings retirement plan (in Japan) as well. I was also wondering if her employer (private) retirement savings have to be reported to the IRS and if they're are taxable in the US.

your wife will have the two pensions and she lives in US.
primarily, these two are independently taxed.
if the Japanese pension is larger than 1080000 yen, income tax will be temporarily deducted.
since she is a resident of US, she have to file the sum of both pensions, according to US law (I don't know US law exactly.)
if some tax is deducted from Japanese pension, she can claim that amount from her US tax, to prevent double taxation.
if she does not file the Japanese pension in US, it means she makes a false tax return.

Thanks Ken, I agree, she will file form 1040 showing amount she received from Japan, I think it should be posted on line 16b (taxable pensions). Her pension right now is only 350,000 Yen, I don't think any tax was deducted in Japan, so she can't claim credit in the US.
I was just wondering if line 16 b should be used for reporting foreign pensions or line 21 (Other Income). Thank you all.

https://www.nenkin.go.jp/oshirase/topics/2015/20151218.files/0216.pdf
the above picture is an example of the recent certificate .
源泉徴収税額, い(circle filled with black) is the tax deducted.