* Q3 net profit Y163.8 bln vs Y178.9 bln year earlier

* Keeps full-year net profit forecast at Y400 bln

* Credit-related costs Y234.8 bln for nine months through Dec

TOKYO, Feb 2 (Reuters) - Sumitomo Mitsui Financial Group Inc (SMFG), Japan's second-largest lender by assets, reported a 8.4% drop in third-quarter net profit on Tuesday primarily due to an increase in credit-related costs.

SMFG posted a profit of 163.8 billion yen ($1.56 billion) for the three months through December compared with 178.9 billion yen in the year-ago period, according to Reuters calculations based on nine-month cumulative figures disclosed in an exchange filing.

SMFG reiterated its profit view of 400 billion yen for the full year through March. That compared with the 500.1 billion yen average of 12 analysts' estimates compiled by Refinitiv.

The lender, which already exceeded its annual profit target, kept its full-year forecast because the situation is becoming "more and more uncertain" due to the coronavirus outbreak, according to a spokesman for the company.

Profits at Japanese banks, already reeling from years of negative interest rates and shrinking population, were expected to be pressured by a surge in credit losses due to the COVID-19 pandemic.

SMFG booked 234.8 billion yen credit-related costs for the nine months through December, up from 96.5 billion yen in the same period a year ago.

Although the credit-related costs weighed down its profit, they were smaller-than-expected as the lender had estimated 450 billion yen of the costs for the current financial year.

The lower credit costs augurs well for the earnings prospects of the local banks with a recovery expected in the world's third-largest economy, which suffered its biggest post-war slump in April-June last year.

Japan's economy will likely recover to levels before the COVID-19 pandemic as early as March next year, Bank of Japan Governor Haruhiko Kuroda said last month.

The number of bankruptcies in Japan came in at 1,751 in the third quarter, or a 20.8% drop from a year earlier, according to research firm Tokyo Shoko Research.

($1 = 104.9900 yen)

(Reporting by Takashi Umekawa; Editing by Christian Schmollinger, Kim Coghill and Amy Caren Daniel)