Free Writing Prospectus (to the

Filed Pursuant to Rule 433

Preliminary Prospectus

Registration Statement Nos.

333-174438

Supplement dated November 13, 2012)

333-174438-04

Issuer:

Principal Financial Group, Inc.

Expected Ratings
(Moody’s / S&P / Fitch)*:

A3 (Negative) / BBB+ (Negative) / A- (Negative)

Issue:

1.850% Senior Notes due 2017 fully and unconditionally guaranteed by Principal Financial Services, Inc.

Offering Size:

$300,000,000

Coupon:

1.850% per annum

Trade Date:

November 13, 2012

Settlement Date:

November 16, 2012

Maturity Date:

November 15, 2017

Treasury Benchmark:

UST 0.750% due October 31, 2017

US Treasury Price:

100-20

US Treasury Yield:

0.622%

Spread to Treasury:

+125 basis points

Re-offer Yield:

1.872%

Price to Public (Issue Price):

99.896%

Net Proceeds to Issuer
(before Expenses):

$297,888,000

Interest Payment Dates:

Semi-annually on May 15 and November 15, commencing on May 15, 2013

Optional Redemption:

At any time in whole or in part at greater of par

and make-whole call at a discount rate of Treasury plus 20 basis points, plus accrued and unpaid interest on the date of redemption

Special Mandatory Redemption:

If (i) the Cuprum acquisition is not completed in accordance with the SPA on or prior to November 19, 2013, or (ii) prior to such date, the SPA is terminated, the issuer will redeem all of the Notes on the Special Mandatory Redemption Date at the Special Mandatory Redemption Price.

‘‘SPA’’ means the Sale and Purchase Promise Agreement, dated October 5, 2012, by and among Empresas Penta S.A. and Inversiones Banpenta Limitada, as promising sellers, and Principal Financial Services, Inc. as promising buyer, as the same may be amended.

“Special Mandatory Redemption Date” means the earlier to occur of (i) December 19, 2013 if the Cuprum acquisition has not been completed on or prior to November 19, 2013 or (ii) the 30th day (or if such day is not a business day, the first business day thereafter) following the termination of the SPA.

“Special Mandatory Redemption Price” means 101% of the aggregate principal amount of the Notes together with accrued and unpaid interest on the Notes from the date of initial issuance (or the most recent interest payment date on which interest was paid) to but excluding the Special Mandatory Redemption Date.

CUSIP/ISIN:

74251VAG7 / US74251VAG77

Joint Book-Running Managers:

Credit Suisse Securities (USA) LLC, Deutsche Bank Securities Inc., Goldman, Sachs & Co. and UBS Securities LLC

Senior Co-Managers:

Merrill Lynch, Pierce, Fenner & Smith Incorporated and Morgan Stanley & Co. LLC

Co-Managers:

HSBC Securities (USA) Inc., RBS Securities Inc., Santander Investment Securities Inc., Wells Fargo Securities, LLC and The Williams Capital Group, L.P.

Issuer:

Principal Financial Group, Inc.

Expected Ratings
(Moody’s / S&P / Fitch)*:

A3 (Negative) / BBB+ (Negative) / A- (Negative)

Issue:

3.125% Senior Notes due 2023 fully and unconditionally guaranteed by Principal Financial Services, Inc.

Offering Size:

$300,000,000

Coupon:

3.125% per annum

Trade Date:

November 13, 2012

Settlement Date:

November 16, 2012

Maturity Date:

May 15, 2023

Treasury Benchmark:

UST 1.625% due November 15, 2022

US Treasury Price:

100-10

US Treasury Yield:

1.591%

Spread to Treasury:

+155 basis points

Re-offer Yield:

3.141%

Price to Public (Issue Price):

99.858%

Net Proceeds to Issuer
(before Expenses):

$297,624,000

Interest Payment Dates:

Semi-annually on May 15 and November 15, commencing on May 15, 2013

Optional Redemption:

At any time in whole or in part at greater of par and make-whole call at a discount rate of Treasury plus 20 basis points, plus accrued and unpaid interest on the date of redemption

Special Mandatory Redemption:

If (i) the Cuprum acquisition is not completed in accordance with the SPA on or prior to November 19, 2013, or (ii) prior to such date, the SPA is terminated, the issuer will redeem all of the Notes on the Special Mandatory Redemption Date at the Special Mandatory Redemption Price.

‘‘SPA’’ means the Sale and Purchase Promise Agreement, dated October 5, 2012, by and among Empresas Penta S.A. and Inversiones Banpenta Limitada, as promising sellers, and Principal Financial Services, Inc. as promising buyer, as the same may be amended.

“Special Mandatory Redemption Date” means the earlier to occur of (i) December 19, 2013 if the Cuprum acquisition has not been completed on or prior to November 19, 2013 or (ii) the 30th day (or if such day is not a business day, the first business day thereafter) following the termination of the SPA.

“Special Mandatory Redemption Price” means 101% of the aggregate principal amount of the Notes together with accrued and unpaid interest on the Notes from the date of initial issuance (or the most recent interest payment date on which interest was paid) to but excluding the Special Mandatory Redemption Date.

CUSIP/ISIN:

74251VAH5 / US74251VAH50

Joint Book-Running Managers:

Credit Suisse Securities (USA) LLC, Deutsche Bank Securities Inc., Goldman, Sachs & Co. and UBS Securities LLC

Senior Co-Managers:

Merrill Lynch, Pierce, Fenner & Smith Incorporated and Morgan Stanley & Co. LLC

Co-Managers:

HSBC Securities (USA) Inc., RBS Securities Inc., Santander Investment Securities Inc., Wells Fargo Securities, LLC and The Williams Capital Group, L.P.

4.350% Senior Notes due 2043

Issuer:

Principal Financial Group, Inc.

Expected Ratings
(Moody’s / S&P / Fitch)*:

A3 (Negative) / BBB+ (Negative) / A- (Negative)

Issue:

4.350% Senior Notes due 2043 fully and unconditionally guaranteed by Principal Financial Services, Inc.

Offering Size:

$300,000,000

Coupon:

4.350% per annum

Trade Date:

November 13, 2012

Settlement Date:

November 16, 2012

Maturity Date:

May 15, 2043

Treasury Benchmark:

UST 2.750% due August 15, 2042

US Treasury Price:

100-22+

US Treasury Yield:

2.715%

Spread to Treasury:

+165 basis points

Re-offer Yield:

4.365%

Price to Public (Issue Price):

99.749%

Net Proceeds to Issuer
(before Expenses):

$296,622,000

Interest Payment Dates:

Semi-annually on May 15 and November 15, commencing on May 15, 2013

Optional Redemption:

At any time in whole or in part at greater of par and make-whole call at a discount rate of Treasury plus 25 basis points, plus accrued and unpaid interest on the date of redemption

Special Mandatory Redemption:

If (i) the Cuprum acquisition is not completed in accordance with the SPA on or prior to November 19, 2013, or (ii) prior to such date, the SPA is terminated, the issuer will redeem all of the Notes on the Special Mandatory Redemption Date at the Special Mandatory Redemption Price.

‘‘SPA’’ means the Sale and Purchase Promise Agreement, dated October 5, 2012, by and among Empresas Penta S.A. and Inversiones Banpenta Limitada, as promising sellers, and Principal Financial Services, Inc. as promising buyer, as the same may be amended.

“Special Mandatory Redemption Date” means the earlier to occur of (i) December 19, 2013 if the Cuprum acquisition has not been completed on or prior to November 19, 2013 or (ii) the 30th day (or if such day is not a business day, the first business day thereafter) following the termination of the SPA.

“Special Mandatory Redemption Price” means 101% of the aggregate principal amount of the Notes together with accrued and unpaid interest on the Notes from the date of initial issuance (or the most recent interest payment date on which interest was paid) to but excluding the Special Mandatory Redemption Date.

CUSIP/ISIN:

74251VAJ1 / US74251VAJ17

Joint Book-Running Managers:

Credit Suisse Securities (USA) LLC, Deutsche Bank Securities Inc., Goldman, Sachs & Co. and UBS Securities LLC

Senior Co-Managers:

Merrill Lynch, Pierce, Fenner & Smith Incorporated and Morgan Stanley & Co. LLC

Co-Managers:

HSBC Securities (USA) Inc., RBS Securities Inc., Santander Investment Securities Inc., Wells Fargo Securities, LLC and The Williams Capital Group, L.P.