(Adds comment on credit cards, impact of proposed tax law changes)
By David Henry
NEW YORK, Dec 6 (Reuters) - Citigroup Inc expects its fourth-quarter markets revenue to be lower by a "high-teens" percentage from a year earlier, Chief Financial Officer John Gerspach said on Wednesday.
Speaking at an investor conference held by bank stock analysts at Goldman Sachs, Gerspach said the decline is mostly due to lower trading in fixed income and compares with an especially strong period in 2016.
On Tuesday executives from JPMorgan Chase & Co and Bank of American Corp said their trading revenues are running about 15 percent less than a year earlier.
Gerspach also said he expects fourth-quarter revenue from Citi-branded credit cards in North America to be "flattish" compared with a year earlier.
This year, Citigroup stepped up marketing of credit cards that promised as much as 21 months without interest charges on balances transferred from other cards, in response to aggressive competition from rivals marketing cards emphasizing spending rewards.
Gerspach also updated earlier estimates of the impact on Citigroup from tax law changes proposed in Washington. Lower tax rates and changes in taxation of income earned overseas are expected to ultimately yield higher returns, but could bring a one-time charge to earnings of about $20 billion, he said.
About $16 billion to $17 billion of that charge would be to write down the value of deferred tax assets on Citigroup's balance sheet. In July, Citigroup had estimated the charge at $15 billion, but that was with corporate taxes going down to 25 percent, instead of the 20 percent rate Gerspach used on Wednesday.
Taxes on repatriating foreign income could run to about $4 billion, but be covered by deferred tax assets and not require cash payments, he said.
Return on tangible common equity could ultimately rise by "a couple" of percent points, he said.
Analysts have said they expected Citigroup to benefit less than other banks from the proposed tax changes. (Reporting by David Henry in New York; Editing by Susan Thomas)