<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 SIX MONTHS
ENDED MARCH 31, 2000, AND IS QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH
FINANCIAL STATEMENTS.
</LEGEND>
<MULTIPLIER> 1,000

<S>                             <C>
<PERIOD-TYPE>                   6-MOS
<FISCAL-YEAR-END>                          SEP-30-2000
<PERIOD-START>                             OCT-01-1999
<PERIOD-END>                               MAR-31-2000
<CASH>                                          81,004
<INT-BEARING-DEPOSITS>                          21,655
<FED-FUNDS-SOLD>                                11,025
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    729,408
<INVESTMENTS-CARRYING>                          68,040
<INVESTMENTS-MARKET>                            65,554
<LOANS>                                      1,732,764
<ALLOWANCE>                                     15,369
<TOTAL-ASSETS>                               2,829,495
<DEPOSITS>                                   1,608,271
<SHORT-TERM>                                   513,138
<LIABILITIES-OTHER>                             17,337
<LONG-TERM>                                    526,850
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                        27,261
<OTHER-SE>                                     136,638
<TOTAL-LIABILITIES-AND-EQUITY>               2,829,495
<INTEREST-LOAN>                                 74,899
<INTEREST-INVEST>                               27,428
<INTEREST-OTHER>                                 1,198
<INTEREST-TOTAL>                               103,525
<INTEREST-DEPOSIT>                              29,001
<INTEREST-EXPENSE>                              56,879
<INTEREST-INCOME-NET>                           46,646
<LOAN-LOSSES>                                    1,100
<SECURITIES-GAINS>                                   6
<EXPENSE-OTHER>                                 36,789
<INCOME-PRETAX>                                 17,533
<INCOME-PRE-EXTRAORDINARY>                      11,343
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                    11,343
<EPS-BASIC>                                       0.72
<EPS-DILUTED>                                     0.71
<YIELD-ACTUAL>                                    3.64
<LOANS-NON>                                     12,005
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                14,123
<CHARGE-OFFS>                                      820
<RECOVERIES>                                       188
<ALLOWANCE-CLOSE>                               15,369
<ALLOWANCE-DOMESTIC>                            11,010
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          4,359


</TABLE>