Exhibit 12

MARSHALL & ILSLEY CORPORATION

Computation of Ratio of Earnings to Fixed Charges

($000s)



|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|-------------------------------------------------------------------------------------------------------------- |  | ------------------------ | --------- | - | ---- | - | --------- | ---- |  | - | --------- | - |  | ---- | --------- | - |  | - | --------- | -
|                                                                                                               |  | Years Ended December 31, |          
|                                                                                                               |  | 2005                     |           |   | 2004 |   |           | 2003 |  |   | 2002      |   |  | 2001 |          
|Earnings:                                                                                                      |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings before income taxes, extraordinary items and cumulative effect of changes in accounting principles    |  | $                        | 1,090,367 |   |      | $ | 944,966   |      |  | $ | 758,387   |   |  | $    | 718,592   |   |  | $ | 501,045   |  
|                                                                                                               |  |                          |           |   |     
|Fixed charges, excluding interest on deposits                                                                  |  |                          | 463,209   |   |      |   | 281,244   |      |  |   | 267,379   |   |  |      | 301,518   |   |  |   | 321,059   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings including fixed charges but excluding interest on deposits                                            |  |                          | 1,553,576 |   |      |   | 1,226,210 |      |  |   | 1,025,766 |   |  |      | 1,020,110 |   |  |   | 822,104   |  
|                                                                                                               |  |                          |           |   |     
|Interest on deposits                                                                                           |  |                          | 544,920   |   |      |   | 276,102   |      |  |   | 228,216   |   |  |      | 283,385   |   |  |   | 566,899   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Earnings including fixed charges and interest on deposits                                                      |  | $                        | 2,098,496 |   |      | $ | 1,502,312 |      |  | $ | 1,253,982 |   |  | $    | 1,303,495 |   |  | $ | 1,389,003 |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed Charges:                                                                                                 |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Interest Expense:                                                                                              |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Short-term borrowings                                                                                          |  | $                        | 106,333   |   |      | $ | 61,256    |      |  | $ | 81,070    |   |  | $    | 150,310   |   |  | $ | 188,587   |  
|Long-term borrowings                                                                                           |  |                          | 330,144   |   |      |   | 196,440   |      |  |   | 163,348   |   |  |      | 127,343   |   |  |   | 110,842   |  
|One-third of rental expense for all operating leases (the amount deemed representative of the interest factor) |  |                          | 26,732    |   |      |   | 23,548    |      |  |   | 22,961    |   |  |      | 23,865    |   |  |   | 21,630    |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed charges excluding interest on deposits                                                                   |  |                          | 463,209   |   |      |   | 281,244   |      |  |   | 267,379   |   |  |      | 301,518   |   |  |   | 321,059   |  
|Interest on deposits                                                                                           |  |                          | 544,920   |   |      |   | 276,102   |      |  |   | 228,216   |   |  |      | 283,385   |   |  |   | 566,899   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Fixed charges including interest on deposits                                                                   |  | $                        | 1,008,129 |   |      | $ | 557,346   |      |  | $ | 495,595   |   |  | $    | 584,903   |   |  | $ | 887,958   |  
|                                                                                                               |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|Ratio of Earnings to Fixed Charges:                                                                            |  |                          |           |   |      |   |           |      |  |   |           |   |  |      |           |   |  |   |           |  
|                                                                                                               |  |                          |           |   |     
|Excluding interest on deposits                                                                                 |  |                          | 3.35      | x |      |   | 4.36      | x    |  |   | 3.84      | x |  |      | 3.38      | x |  |   | 2.56      | x
|                                                                                                               |  |                          |           |   |     
|Including interest on deposits                                                                                 |  |                          | 2.08      | x |      |   | 2.70      | x    |  |   | 2.53      | x |  |      | 2.23      | x |  |   | 1.56      | x