<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, 1999, 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-30-2000
<PERIOD-START>                             OCT-01-1999
<PERIOD-END>                               DEC-31-1999
<CASH>                                         104,415
<INT-BEARING-DEPOSITS>                           9,647
<FED-FUNDS-SOLD>                                     0
<TRADING-ASSETS>                                     0
<INVESTMENTS-HELD-FOR-SALE>                    747,982
<INVESTMENTS-CARRYING>                          68,896
<INVESTMENTS-MARKET>                            66,453
<LOANS>                                      1,672,315
<ALLOWANCE>                                     15,182
<TOTAL-ASSETS>                               2,782,568
<DEPOSITS>                                   1,598,190
<SHORT-TERM>                                   319,978
<LIABILITIES-OTHER>                             15,399
<LONG-TERM>                                    677,281
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                        33,297
<OTHER-SE>                                     162,043
<TOTAL-LIABILITIES-AND-EQUITY>               2,782,568
<INTEREST-LOAN>                                 36,297
<INTEREST-INVEST>                               13,360
<INTEREST-OTHER>                                   724
<INTEREST-TOTAL>                                50,381
<INTEREST-DEPOSIT>                              14,791
<INTEREST-EXPENSE>                              27,283
<INTEREST-INCOME-NET>                           23,098
<LOAN-LOSSES>                                      550
<SECURITIES-GAINS>                                   0
<EXPENSE-OTHER>                                 18,443
<INCOME-PRETAX>                                  8,395
<INCOME-PRE-EXTRAORDINARY>                       8,395
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                                     5,462
<EPS-BASIC>                                       0.34
<EPS-DILUTED>                                     0.34
<YIELD-ACTUAL>                                    3.67
<LOANS-NON>                                     10,950
<LOANS-PAST>                                         0
<LOANS-TROUBLED>                                     0
<LOANS-PROBLEM>                                      0
<ALLOWANCE-OPEN>                                14,123
<CHARGE-OFFS>                                      374
<RECOVERIES>                                       105
<ALLOWANCE-CLOSE>                               15,182
<ALLOWANCE-DOMESTIC>                            10,310
<ALLOWANCE-FOREIGN>                                  0
<ALLOWANCE-UNALLOCATED>                          4,872


</TABLE>