Filed under Rule 424(b)(3), Registration Statement No. 333-275151

Pricing Supplement No. 642 - Dated Monday, August 11, 2025 (To: Prospectus Dated October 24, 2023 and Prospectus Supplement Dated October 27, 2023)

CUSIP Number

Principal Amount

Selling Price

Gross Concession

Net Proceeds

Coupon Type

Coupon Rate

Coupon Frequency

Maturity Date

1st Coupon Date

1st Coupon Amount

Survivor's Option

Product Ranking

63743F3T1

[ ]

100.000%

0.550%

[ ]

Fixed

3.950%

Monthly

08/15/2027

09/15/2025

$2.63

Yes

Senior Unsecured Notes

Redemption Information:Non-Callable

	Offering Date: Monday, August 11, 2025 through Monday, August 18, 2025	National Rural Utilities Cooperative Finance Corp
National Rural Utilities Cooperative Finance Corp	Trade Date: Monday, August 18, 2025 @12:00 PM ET
	Settle Date: Thursday, August 21, 2025	Prospectus dated October 24, 2023 and
	Minimum Denomination/Increments:$1,000.00/$1,000.00	Prospectus Supplement Dated: October 27, 2023
	Initial trades settle flat and clear SDFS: DTC Book Entry only
	DTC Number: 0235 via RBC Dain Rauscher Inc.
	Agents: InspereX LLC, Citigroup Global Markets Inc., Wells Fargo Clearing Services, LLC, RBC Capital Markets, LLC
	Trustee: U.S. Bank Trust Company, National Association
	If the maturity date or an interest payment date for any note is not a business day (as term is defined in prospectus), principal, premium, if any, and interest for that note is paid on the next business day, and no interest will accrue from, and after, the maturity date or interest payment date.
	Notes will be sold to you at the selling price specified in this Pricing Supplement. The Purchasing Agent shall purchase notes from us at the selling price less the applicable gross concession specified in this Pricing Supplement. The Purchasing Agent may resell the notes it purchases to the agents and selected dealers at the selling price less a concession that, at the discretion of the Purchasing Agent, may be less than or equal to the gross concession received by the Purchasing Agent. Notes purchased by the agents and selected dealers on behalf of level-fee [investment or advisory] accounts may be sold to such accounts at the selling price less the applicable concession, and such agents and selected dealers shall not retain, as compensation, any portion of such concession.
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