INDEX 400 STOCK FUND

Fund Overview

Adviser:

Mason Street Advisors, LLC

Objective/Focus:

Invests substantially all of its assets in the stocks in the S&P MidCap 400® Index, which is an unmanaged index of 400 selected common stocks compiled by Standard & Poor’s® and weighted toward medium market capitalizations. The objective is to achieve investment results that approximate the performance of the S&P MidCap 400® Index.

Asset Class:

Mid-Cap Stocks

Style:

Blend/Market-Oriented

Investing in small company stocks involves a greater degree of risk than investing in medium or large company stocks. Indices are unmanaged, cannot be invested in directly.

Fund Facts as of 03/31/18

Fund Inception

04-30-1999

First Available for Variable Annuity

04-30-1999

First Available for Variable Life

06-30-1999

Net Assets

$887.7 Million

Top 10 Portfolio Holdings % of Net Assets

MSCI, Inc.

0.8%

Broadridge Financial Solutions, Inc.

0.7%

ABIOMED, Inc.

0.7%

Teleflex, Inc.

0.6%

IDEX Corp.

0.6%

Steel Dynamics, Inc.

0.6%

Copart, Inc.

0.6%

Domino's Pizza, Inc.

0.6%

Old Dominion Freight Line, Inc.

0.6%

Keysight Technologies, Inc.

0.6%

Total % of Net Assets

6.4%

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Disclosed Holdings

Sector Weightings % of Equities

Financials

17.8%

Information Technology

17.5%

Industrials

15.5%

Consumer Discretionary

12.0%

Real Estate

8.8%

Before investing in a variable product, you should carefully consider the objectives, risks and charges associated with its investment options. For this and other information about a Contract, you should obtain the appropriate Contract and underlying fund prospectuses by contacting your Northwestern Mutual Financial Representative. Read the prospectuses carefully before you invest.

Mason Street Advisors, LLC (MSA) is the principal investment adviser for all the Portfolios in the Northwestern Mutual Series Fund (Series Fund). (Portfolios in the Series Fund are identified by the parenthetical next to the portfolio name.) MSA has engaged and oversees sub-advisers who provide day-to-day management for certain of the Series Fund Portfolios. Each sub-adviser may be replaced without the approval of shareholders. Please see the prospectus for more information. Additional fund options are advised by Russell Investments, Fidelity Investments, Neuberger Berman Investment Advisers LLC and Credit Suisse Asset Management, LLC

All securities are offered through Northwestern Mutual Investment Services LLC, (NMIS), Suite 600, 611 E. Wisconsin Avenue, Milwaukee, WI 53202, 1-866-664-7737. Member FINRA and SIPC. NMIS is a subsidiary of Northwestern Mutual.