<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 QUARTER ENDED
DECEMBER 31, 1997 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   3-MOS
<FISCAL-YEAR-END>                          SEP-30-1998
<PERIOD-START>                             OCT-01-1997
<PERIOD-END>                               DEC-31-1997
<CASH>                                          46,191
<INT-BEARING-DEPOSITS>                               0
<FED-FUNDS-SOLD>                                     0
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    582,469
<INVESTMENTS-CARRYING>                          96,515
<INVESTMENTS-MARKET>                            94,646
<LOANS>                                      1,150,680
<ALLOWANCE>                                      8,572
<TOTAL-ASSETS>                               1,982,317
<DEPOSITS>                                   1,154,914
<SHORT-TERM>                                   556,413
<LIABILITIES-OTHER>                             11,508
<LONG-TERM>                                    126,084
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                         1,615
<OTHER-SE>                                     131,783
<TOTAL-LIABILITIES-AND-EQUITY>               1,982,317
<INTEREST-LOAN>                                 25,173
<INTEREST-INVEST>                               12,251
<INTEREST-OTHER>                                   444
<INTEREST-TOTAL>                                37,868
<INTEREST-DEPOSIT>                              13,073
<INTEREST-EXPENSE>                              23,290
<INTEREST-INCOME-NET>                           14,578
<LOAN-LOSSES>                                      200
<SECURITIES-GAINS>                                 136
<EXPENSE-OTHER>                                 11,069
<INCOME-PRETAX>                                  7,937
<INCOME-PRE-EXTRAORDINARY>                       5,161
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                     5,161
<EPS-PRIMARY>                                     0.64
<EPS-DILUTED>                                     0.63
<YIELD-ACTUAL>                                    3.07
<LOANS-NON>                                      6,475
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                 8,667
<CHARGE-OFFS>                                      411
<RECOVERIES>                                       116
<ALLOWANCE-CLOSE>                                8,572
<ALLOWANCE-DOMESTIC>                             4,713
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          3,859
        

</TABLE>