<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 THREE MONTHS
ENDED DECEMBER 31, 1998 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-30-1999
<PERIOD-START>                             OCT-01-1998
<PERIOD-END>                               DEC-31-1998
<CASH>                                          70,245
<INT-BEARING-DEPOSITS>                          16,441
<FED-FUNDS-SOLD>                                14,451
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    825,646
<INVESTMENTS-CARRYING>                          81,654
<INVESTMENTS-MARKET>                            81,462
<LOANS>                                      1,352,612
<ALLOWANCE>                                     13,527
<TOTAL-ASSETS>                               2,601,561
<DEPOSITS>                                   1,540,000
<SHORT-TERM>                                   135,228
<LIABILITIES-OTHER>                             29,453
<LONG-TERM>                                    721,507
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                        36,715
<OTHER-SE>                                     138,568
<TOTAL-LIABILITIES-AND-EQUITY>               2,601,561
<INTEREST-LOAN>                                 31,773
<INTEREST-INVEST>                               11,721
<INTEREST-OTHER>                                 1,582
<INTEREST-TOTAL>                                45,076
<INTEREST-DEPOSIT>                              14,664
<INTEREST-EXPENSE>                              24,484
<INTEREST-INCOME-NET>                           20,592
<LOAN-LOSSES>                                      498
<SECURITIES-GAINS>                               (160)
<EXPENSE-OTHER>                                 16,773
<INCOME-PRETAX>                                 11,162
<INCOME-PRE-EXTRAORDINARY>                       7,368
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                     7,368
<EPS-PRIMARY>                                     0.47
<EPS-DILUTED>                                     0.46
<YIELD-ACTUAL>                                    3.58
<LOANS-NON>                                     12,392
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                13,224
<CHARGE-OFFS>                                      318
<RECOVERIES>                                       123
<ALLOWANCE-CLOSE>                               13,527
<ALLOWANCE-DOMESTIC>                             9,883
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          3,644
        

</TABLE>