<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, 1999, 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-30-1999
<PERIOD-START>                             OCT-01-1998
<PERIOD-END>                               JUN-30-1999
<CASH>                                          67,588
<INT-BEARING-DEPOSITS>                           6,079
<FED-FUNDS-SOLD>                                17,800
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    751,937
<INVESTMENTS-CARRYING>                          72,869
<INVESTMENTS-MARKET>                            72,180
<LOANS>                                      1,418,279
<ALLOWANCE>                                     13,803
<TOTAL-ASSETS>                               2,474,158
<DEPOSITS>                                   1,544,787
<SHORT-TERM>                                    44,576
<LIABILITIES-OTHER>                             17,450
<LONG-TERM>                                    690,799
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                        31,435
<OTHER-SE>                                     145,111
<TOTAL-LIABILITIES-AND-EQUITY>               2,474,158
<INTEREST-LOAN>                                 93,656
<INTEREST-INVEST>                               37,065
<INTEREST-OTHER>                                 2,721
<INTEREST-TOTAL>                               133,442
<INTEREST-DEPOSIT>                              41,643
<INTEREST-EXPENSE>                              71,206
<INTEREST-INCOME-NET>                           62,236
<LOAN-LOSSES>                                    1,498
<SECURITIES-GAINS>                                  72
<EXPENSE-OTHER>                                 50,293
<INCOME-PRETAX>                                 33,709
<INCOME-PRE-EXTRAORDINARY>                      22,065
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                    22,065
<EPS-BASIC>                                       1.41
<EPS-DILUTED>                                     1.38
<YIELD-ACTUAL>                                    3.60
<LOANS-NON>                                     10,522
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                13,224
<CHARGE-OFFS>                                    1,248
<RECOVERIES>                                       329
<ALLOWANCE-CLOSE>                               13,803
<ALLOWANCE-DOMESTIC>                             8,570
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          5,233


</TABLE>