| Exhibit 12.2                                                                                                                                      |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|---------------------------------------------------------------------------------------------------------------------------------------------------|--------|-----------------------|--------|--------|----------------------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|--------|
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| INTERSTATE POWER AND LIGHT COMPANY                                                                                                                |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| RATIO OF EARNINGS TO FIXED CHARGES AND RATIO OF EARNINGS TO COMBINED FIXED CHARGES                                                                |   |
|      AND PREFERRED DIVIDEND REQUIREMENTS                                                                                      |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   | Nine Months           |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   | Ended Sep. 30,        |   |   | Years Ended Dec. 31, |   |
|                                                                                                                                              |   | 2009                  |   |   | 2008                 |   |   | 2008   |   |   | 2007   |   |   | 2006   |   |   | 2005   |   |   | 2004   |   |
|                                                                                                                                              |   | (dollars in millions) |   |
| EARNINGS:                                                                                                                                         |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Net income                                                                                                                                        |   | $                     | 133.9  |   |                 | $      | 112.8  |   |   | $      | 141.6  |   |   | $      | 290.3  |   |   | $      | 172.4  |   |   | $ | 165.1 |   |   | $ | 125.7 |   |
| Income taxes (a)                                                                                                                                  |   |                  | 16.7   |   |                 |   | 46.9   |   |   |   | 52.6   |   |   |   | 186.8  |   |   |   | 69.4   |   |   |   | 80.8 |   |   |   | 61.7 |   |
| Income before income taxes                                                                                                                        |   |                  | 150.6  |   |                 |   | 159.7  |   |   |   | 194.2  |   |   |   | 477.1  |   |   |   | 241.8  |   |   |   | 245.9 |   |   |   | 187.4 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Fixed charges as defined                                                                                                                          |   |                  | 57.2   |   |                 |   | 45.7   |   |   |   | 63.7   |   |   |   | 65.8   |   |   |   | 73.3   |   |   |   | 72.5 |   |   |   | 72.3 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Total earnings as defined                                                                                                                         |   | $                     | 207.8  |   |                 | $      | 205.4  |   |   | $      | 257.9  |   |   | $      | 542.9  |   |   | $      | 315.1  |   |   | $ | 318.4 |   |   | $ | 259.7 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| FIXED CHARGES:                                                                                                                                    |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Interest expense                                                                                                                                  |   | $                     | 56.4   |   |                 | $      | 44.2   |   |   | $      | 61.9   |   |   | $      | 64.3   |   |   | $      | 71.8   |   |   | $ | 67.7 |   |   | $ | 67.9 |   |
| Estimated interest component of rent expense                                                                                                      |   |                  | 0.8    |   |                 |   | 1.5    |   |   |   | 1.8    |   |   |   | 1.5    |   |   |   | 1.5    |   |   |   | 4.8 |   |   |   | 4.4 |   |
| Total fixed charges as defined                                                                                                                    |   | $                     | 57.2   |   |                 | $      | 45.7   |   |   | $      | 63.7   |   |   | $      | 65.8   |   |   | $      | 73.3   |   |   | $ | 72.5 |   |   | $ | 72.3 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Ratio of Earnings to Fixed Charges                                                                                                                |   |                  | 3.63   |   |                 |   | 4.49   |   |   |   | 4.05   |   |   |   | 8.25   |   |   |   | 4.30   |   |   |   | 4.39 |   |   |   | 3.59 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Preferred dividend requirements (pre-tax basis) (b)                                                                                               |   | $                     | 12.9   |   |                 | $      | 16.3   |   |   | $      | 21.1   |   |   | $      | 25.3   |   |   | $      | 21.6   |   |   | $ | 22.9 |   |   | $ | 23.0 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Fixed charges and preferred dividend requirements                                                                                                 |   | $                     | 70.1   |   |                 | $      | 62.0   |   |   | $      | 84.8   |   |   | $      | 91.1   |   |   | $      | 94.9   |   |   | $ | 95.4 |   |   | $ | 95.3 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| Ratio of Earnings to Combined Fixed Charges and                                                                                                   |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
|    Preferred Dividend Requirements                                                                                                 |   |                  | 2.96   |   |                 |   | 3.31   |   |   |   | 3.04   |   |   |   | 5.96   |   |   |   | 3.32   |   |   |   | 3.34 |   |   |   | 2.73 |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| (a) Includes net interest related to unrecognized tax benefits.                                                                                   |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |
|                                                                                                                                              |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |
| (b) Preferred dividend requirements (pre-tax basis) are computed by dividing the preferred dividend requirements by one hundred percent minus the |   |
| respective year-to-date effective income tax rate.                                                                                                |   |                  |   |   |                 |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |   |