<TABLE> <S> <C>

<PAGE>
<ARTICLE> 9
<LEGEND>
This schedule contains financial information extracted from the consolidated
financial statements of InterWest Bancorp, Inc. as of and for the nine months
ended June 30, 1998 and is qualified in its entirety by reference to such
financial statements.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   9-MOS
<FISCAL-YEAR-END>                          SEP-30-1998
<PERIOD-START>                             OCT-01-1997
<PERIOD-END>                               JUN-30-1998
<CASH>                                          66,322
<INT-BEARING-DEPOSITS>                          14,382
<FED-FUNDS-SOLD>                                13,096
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    600,576
<INVESTMENTS-CARRYING>                          91,042
<INVESTMENTS-MARKET>                            89,384
<LOANS>                                      1,440,395
<ALLOWANCE>                                     12,750
<TOTAL-ASSETS>                               2,351,248
<DEPOSITS>                                   1,484,755
<SHORT-TERM>                                   382,539
<LIABILITIES-OTHER>                             24,213
<LONG-TERM>                                    291,743
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                         2,103
<OTHER-SE>                                     165,895
<TOTAL-LIABILITIES-AND-EQUITY>               2,351,248
<INTEREST-LOAN>                                 94,593
<INTEREST-INVEST>                               37,730
<INTEREST-OTHER>                                 2,023
<INTEREST-TOTAL>                               134,346
<INTEREST-DEPOSIT>                              45,466
<INTEREST-EXPENSE>                              75,785
<INTEREST-INCOME-NET>                           58,561
<LOAN-LOSSES>                                    2,366
<SECURITIES-GAINS>                                 649
<EXPENSE-OTHER>                                 50,793
<INCOME-PRETAX>                                 23,968
<INCOME-PRE-EXTRAORDINARY>                      15,235
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                    15,235
<EPS-PRIMARY>                                     0.97
<EPS-DILUTED>                                     0.94
<YIELD-ACTUAL>                                    3.52
<LOANS-NON>                                      7,992
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                11,104
<CHARGE-OFFS>                                      970
<RECOVERIES>                                       325
<ALLOWANCE-CLOSE>                               12,750
<ALLOWANCE-DOMESTIC>                             8,083
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          4,667
        

</TABLE>