QuickLinks -- Click here to rapidly navigate through this document

Filed pursuant to Rule 424(b)(3)
Registration No. 333-109727

Prospectus Supplement No. 1
(To Prospectus Dated October 24, 2003)

$210,000,000
NEW CENTURY FINANCIAL CORPORATION
3.50% CONVERTIBLE SENIOR NOTES DUE 2008
AND THE COMMON STOCK ISSUABLE UPON CONVERSION OF THE NOTES

        This prospectus supplement amends and supplements the prospectus dated October 24, 2003, relating to our 3.50% Convertible Senior Notes Due July 3, 2008 and the shares of our common stock issuable upon conversion of the notes.

        This prospectus supplement is incorporated by reference into, and should be read in conjunction with, the prospectus dated October 24, 2003, including any amendments or supplements to it. This prospectus supplement is not complete without, and may not be delivered or utilized except in connection with, the prospectus, including any amendments or supplements to it.

        See "Risk Factors" beginning on page 8 of the prospectus dated October 24, 2003 to read about factors you should consider before buying the notes.

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities or passed upon the adequacy or accuracy of the prospectus or this prospectus supplement. Any representation to the contrary is a criminal offense.

        This prospectus supplement amends and replaces the table under the heading "Selling Securityholders" beginning on page 61 of the prospectus dated October 24, 2003, with the information in the following table.

The date of this prospectus supplement is November 26, 2003.


SELLING SECURITYHOLDERS

 
    
    
    
    
   Beneficial Ownership After Offering
  
 
    
    
   Number of Shares of Common Stock Held Before Offering(1)
    
  
 
   Aggregate Principal
Amount of Notes
Owned Before
Offering and That May Be Sold
    
    
  
Selling Securityholder
   Percentage of Notes
Outstanding
Before Offering
   Number of
Shares of Common Stock Offered for Sale(1)(2)
   Number of
Shares of
Common Stock(3)
   Percentage of Shares of
Common Stock(3)(4)
  
Akela Capital Master Fund, Ltd.   $ 7,000,000   3.3 % 201,156   201,156   —   *  
Argent Classic Convertible Arbitrage Fund L.P.     4,000,000   1.9   114,946   114,946   —   *  
Argent Classic Convertible Arbitrage Fund (Bermuda) Ltd.     4,000,000   1.9   114,946   114,946   —   *  
Bear, Stearns & Co. Inc.(5)     1,900,000   *   981,866   54,599   927,267   2.7 %
BP Amoco PLC Master Trust     657,000   *   18,879   18,879   —   *  
BNP Paribas Equity Strategies, SNC     4,037,000   1.9   126,517   116,009   10,508   *  
Calamos® Market Neutral Fund — Calamos® Investment Trust     5,000,000   2.4   143,683   143,683   —   *  
Cheyne Fund LP     1,130,000   *   32,472   32,472   —   *  
Cheyne Leveraged Fund LP     660,000   *   18,966   18,966   —   *  
CIP Limited Duration Company     140,000   *   4,023   4,023   —   *  
CNH CA Master Account, L.P.     4,000,000   1.9   114,946   114,946   —   *  
Coastal Convertibles Ltd     500,000   *   14,368   14,368   —   *  
Context Convertible Arbitrage Fund, LP     1,900,000   *   54,599   54,599   —   *  
Context Convertible Arbitrage Offshore, L.T.D.     2,600,000   1.2   74,715   74,715   —   *  
CooperNeff Convertible Strategies (Cayman) Master Fund LP     3,981,000   1.9   114,400   114,400   —   *  
CS Alternative Strategy Limited     70,000   *   2,011   2,011   —   *  
DB Equity Opportunities Master Portfolio Ltd     4,500,000   2.1   129,314   129,314   —   *  
D.E. Shaw Investment Group, L.P.     400,000   *   11,494   11,494   —   *  
D.E. Shaw Valence Portfolios, L.P.     1,600,000   *   45,978   45,978   —   *  
DEAM Convertible Arbitrage     1,500,000   *   43,104   43,104   —   *  
                             

2

Geode U.S. Convertible Arbitrage Fund, a series of Geode Investors, LLC     6,000,000   2.9   172,419   172,419   —   *  
GLG Market Neutral Fund(6)     25,000,000   11.9   718,415   718,415   —   *  
HighBridge International LLC(7)     23,500,000   11.2   675,310   675,310   —   *  
Hotel Union & Hotel Industry of Hawaii Pension Plan     234,000   *   6,724   6,724   —   *  
Jefferies & Company Inc.     5,000   *   143   143   —   *  
JP Morgan Securities Inc.     4,000,000   1.9   114,946   114,946   —   *  
Lyxor / Convertible Arbitrage Fund Limited     247,000   *   7,097   7,097   —   *  
Polaris Vega Fund L.P.     2,000,000   *   57,473   57,473   —   *  
Pyramid Equity Strategies Fund     1,000,000   *   28,736   28,736   —   *  
RBC Alternative Asset, L.P.     150,000   *   13,369   4,310   9,059   *  
Sage Capital     3,450,000   1.6   99,141   99,141   —   *  
San Diego County Employee Retirement Association     1,000,000   *   28,736   28,736   —   *  
Silverback Master, LTD(8)     18,000,000   8.6   517,258   517,258   —   *  
SingleHedge US Convertible Arbitrage Fund     665,000   *   19,109   19,109   —   *  
Sphinx Convertible Arb Fund SPC     259,000   *   7,442   7,442   —   *  
SSI Blended Market Neutral L.P.     468,000   *   13,448   13,448   —   *  
SSI Hedged Convertible Market Neutral L.P.     499,000   *   14,339   14,339   —   *  
Sturgeon Limited     725,000   *   20,834   20,834   —   *  
Sunrise Partners Limited Partnership     15,500,000   7.4   445,417   445,417   —   *  
Whitebox Convertible Arbitrage Partners, LP     6,000,000   2.9   172,419   172,419   —   *  
Xavex Convertible Arbitrage 10 Fund     4,000,000   1.9   114,946   114,946   —   *  
Van Kampen Harbor Fund     2,000,000   *   57,473   57,473   —   *  
Viacom Inc. Pension Plan Master Trust     21,000   *   603   603   —   *  
Zazove Convertible Arbitrage Fund, L.P.     1,000,000   *   28,736   28,736   —   *  
                             

3

Zurich Institutional Benchmarks Master Fund Ltd.     1,357,000   *   38,995   38,995   —   *  
All other holders of the Notes or future transferees, pledgees, donees, assignees or successors of any such holders(9)     47,345,000   22.5   1,360,534 (10) 1,360,534   — (10) *  
   
 
 
 
 
 
 
Totals   $ 210,000,000   100.00 % 6,998,320   6,034,686   946,834   2.8 %
   
 
 
 
 
 
 
*
Less than one percent (1%).

(1)
Assumes conversion of all of the holder's notes based upon the initial conversion price of approximately $34.80 per share of common stock. This is equivalent to a conversion rate of approximately 28.7366 shares per $1,000 principal amount of notes. This conversion rate is subject to adjustment as described under "Description of the Notes—Conversion of Notes." As a result, the number of shares of common stock issuable upon conversion of the notes may increase in the future. In addition, the number of shares of common stock listed for each holder does not include fractional shares. Holders will receive a cash payment for any fractional share resulting from conversion of the notes, as described under "Description of Notes—Conversion of Notes."

(2)
Except as noted, the shares of common stock that may be sold upon conversion of the notes by any selling securityholder will not represent 1% or more of our outstanding common stock.

(3)
Assumes all of the notes and shares of common stock issuable upon their conversion are sold in the offering.

(4)
Based on 33,714,285 shares outstanding as of October 8, 2003. In calculating this amount, we treated as outstanding the number of shares of common stock issuable upon conversion of this selling securityholder's notes, but we did not assume conversion of any other selling securityholder's notes.

(5)
This selling securityholder was an initial purchaser of the notes in our private offering of the notes pursuant to Rule 144A.

(6)
The shares of common stock that may be sold upon conversion of notes by this selling securityholder will represent 2.1% of our outstanding common stock. This percentage is calculated based on Rule 13d-3(d)(i) of the Exchange Act, using 33,714,285 shares of common stock outstanding as of October 8, 2003. In calculating this amount, we treated as outstanding the number of shares of common stock issuable upon conversion of all of this selling securityholder's notes, but we did not assume conversion of any other selling securityholder's notes.

(7)
The shares of common stock that may be sold upon conversion of notes by this selling securityholder will represent 2.0% of our outstanding common stock. This percentage is calculated based on Rule 13d-3(d)(i) of the Exchange Act, using 33,714,285 shares of common stock outstanding as of October 8, 2003. In calculating this amount, we treated as outstanding the number of shares of common stock issuable upon conversion of all of this selling securityholder's notes, but we did not assume conversion of any other selling securityholder's notes.

4

(8)
The shares of common stock that may be sold upon conversion of notes by this selling securityholder will represent 1.5% of our outstanding common stock. This percentage is calculated based on Rule 13d-3(d)(i) of the Exchange Act, using 33,714,285 shares of common stock outstanding as of October 8, 2003. In calculating this amount, we treated as outstanding the number of shares of common stock issuable upon conversion of all of this selling securityholder's notes, but we did not assume conversion of any other selling securityholder's notes.

(9)
New selling securityholders, if any, will be set forth from time to time in post-effective amendments to the registration statement of which this prospectus is a part or supplements to this prospectus, as required.

(10)
Assumes that any other holders of notes, or any future transferees, pledgees, donees or successors of or from any such other holders of notes do not beneficially own any common stock other than the common stock issuable upon conversion of the notes.

        Information concerning the selling securityholders may change from time to time, and any changed information will be set forth in prospectus supplements if and when required.

5




QuickLinks

SELLING SECURITYHOLDERS