<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 FORTHE YEAR ENDED
SEPTEMBER 30, 1998 AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>
<PERIOD-TYPE>                   12-MOS
<FISCAL-YEAR-END>                          SEP-30-1998
<PERIOD-START>                             OCT-01-1997
<PERIOD-END>                               SEP-30-1998
<CASH>                                          74,018
<INT-BEARING-DEPOSITS>                         107,404
<FED-FUNDS-SOLD>                                19,863
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    574,346
<INVESTMENTS-CARRYING>                          87,262
<INVESTMENTS-MARKET>                            87,366
<LOANS>                                      1,359,050
<ALLOWANCE>                                     13,224
<TOTAL-ASSETS>                               2,447,848
<DEPOSITS>                                   1,564,825
<SHORT-TERM>                                    60,157
<LIABILITIES-OTHER>                             28,981
<LONG-TERM>                                    622,233
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                             0
<OTHER-SE>                                     171,652
<TOTAL-LIABILITIES-AND-EQUITY>               2,447,848
<INTEREST-LOAN>                                127,472
<INTEREST-INVEST>                               49,591
<INTEREST-OTHER>                                 3,216
<INTEREST-TOTAL>                               180,279
<INTEREST-DEPOSIT>                              60,841
<INTEREST-EXPENSE>                             101,483
<INTEREST-INCOME-NET>                           78,796
<LOAN-LOSSES>                                    2,807
<SECURITIES-GAINS>                                 813
<EXPENSE-OTHER>                                 66,972
<INCOME-PRETAX>                                 35,490
<INCOME-PRE-EXTRAORDINARY>                      22,642
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                    22,642
<EPS-PRIMARY>                                     1.45
<EPS-DILUTED>                                     1.40
<YIELD-ACTUAL>                                    3.52
<LOANS-NON>                                      8,210
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                11,104
<CHARGE-OFFS>                                    1,290
<RECOVERIES>                                       384
<ALLOWANCE-CLOSE>                               13,224
<ALLOWANCE-DOMESTIC>                             9,325
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          3,899
        

</TABLE>