* Revenue at bond-trading unit seen dropping 22 pct in Q4
* Shares extend losses, down more than 4 percent
* Bank had warned of weak Q4 revenue (Adds detail from statement, share price)
FRANKFURT, Jan 5 (Reuters) - Deutsche Bank will post a small net loss in 2017 after weak trading, low client activity and a 1.5 billion euro ($1.8 billion) negative impact from a tax overhaul in the United States, it said on Friday.
The bank said that the reduction in the U.S. corporate rate to 21 percent from 35 percent would translate into an average tax rate for the whole group at the lower end of a range between 30 percent and 35 percent.
The lower effective tax rate will require a revision to the valuation of deferred tax assets, causing the negative hit to Deutsche's fourth-quarter earnings, it said, adding that it will not have any cash impact.
"Trading conditions in the fourth quarter 2017 were characterised by low volatility in financial markets and low levels of client activity in key businesses," Deutsche Bank said in its statement.
Germany's largest lender has struggled to keep revenue from shrinking and experienced a 10 percent drop in the third quarter. The bank had warned that the fourth quarter could be rough and confirmed that view on Friday.
Revenue at Deutsche Bank's cash-generating bond-trading division were expected to drop 22 percent from a year ago, the bank said.
Deutsche Bank's shares extended losses after the announcement and were down 4.4 percent by 1557 GMT. Before the announcement, shares were down about 2 percent.
The bank is due to report fourth-quarter and full-year earnings on Feb. 2. ($1 = 0.8306 euros) (Reporting by Tom Sims; Editing by Douglas Busvine and David Goodman)