I have a Canadian citizen, resident of Canada.  She received a lump sum distribution fro an inherited IRA.  10% was withheld. I believe the withholding should have been 30% or may be 15%.  I think she needs to file a 1040-NR, compute the US tax on the distribution and pay the additional amount due. I am not sure if the tax should be computed using the tax rates or if it should be a flat 15% (the treaty rate on periodic payments, it appears that IRS regulations state that is immaterial weather the payment is made as a series of payments or in a single lump sum)