February-----, 2018

Medium-Term Senior Notes, Series G

Pricing Supplement No. 2018-CMTNG1016

Filed Pursuant to Rule 424(b)(2)

Registration Statement No. 333-216372

·  During each interest period from and including the issue date to but excluding March   , 2021 (expected to be March 5, 2021), the notes will bear interest at a fixed rate of 4.125% per annum

·  During each interest period commencing on or after March   , 2021 (expected to be March 5, 2021), the notes will bear interest at a floating rate equal to CMS10, as determined on the interest determination date for that interest period, subject to a minimum interest rate of 0.00% per annum.

The amount of interest you receive on each interest payment date for each note you hold will be equal to (i) $1,000 times the applicable interest rate per annum divided by (ii) 4.

After the first three years of the term of the notes, interest payments will vary based on fluctuations in the CMS10, subject to the minimum interest rate specified above. After the first three years, the notes may pay a below-market rate or no interest at all for an extended period of time, or even throughout the entire remaining term.

The description of the notes in this pricing supplement supplements, and, to the extent inconsistent with, replaces the general terms of the notes set forth in the accompanying prospectus supplement and prospectus. The accompanying prospectus supplement and prospectus contain important disclosures that are not repeated in this pricing supplement.

The notes are senior unsecured debt securities issued by Citigroup Inc. under the senior debt indenture described in the accompanying prospectus supplement and prospectus, the payments on which are fully and unconditionally guaranteed by Citigroup Inc. The notes will constitute part of the senior debt of Citigroup Inc. and will rank equally with all other unsecured and unsubordinated debt of Citigroup Inc. The guarantee of payments due on the notes will constitute part of the senior indebtedness of Citigroup Inc. and will rank on an equal basis with all other unsecured debt of Citigroup Inc. other than subordinated debt.

CMS10 on any date of determination is the rate for U.S. dollar interest rate swaps with a 10-year maturity appearing on Reuters page “ICESWAP1” (or any successor page as determined by the calculation agent) as of 11:00 a.m. (New York City time) on that date of determination.

If, however, a rate for CMS10 is not published on Reuters page “ICESWAP1” (or any successor page as determined by the calculation agent) on that date of determination, then the calculation agent will request mid-market semi-annual swap rate quotations from the principal New York City office of five leading swap dealers in the New York City interbank market (the “reference banks”) at approximately 11:00 am, New York City time, on that day. For this purpose, the mid-market semi-annual swap rate means the mean of the bid and offered rates for the semi-annual fixed leg, calculated on a 30/360 day count basis, of a fixed-for-floating U.S. dollar interest rate swap transaction with a 10-year maturity, commencing on that day and in a representative amount with an acknowledged dealer of good credit in the swap market, where the floating leg, calculated on an actual/360 day count basis, is equivalent to U.S. dollar LIBOR with a designated maturity of three months. If at least three quotations are provided, the rate for CMS10 for that day will be the arithmetic mean of the quotations, eliminating the highest quotation (or, in the event of equality, one of the highest) and the lowest quotation (or, in the event of equality, one of the lowest). If fewer than three quotations are provided as requested, a rate for CMS10 will be determined by the calculation agent in good faith and using its reasonable judgment.

CMS10 is calculated by ICE Benchmark Administration Limited based on tradable quotes for U.S. dollar fixed-for-floating interest rate swaps with a 10-year maturity that are sourced from electronic trading venues.

The provisions set forth in this section “—Determination of CMS10” are subject to the discussion in “Discontinuance of CMS10” below.

If the calculation and publication of CMS10 is permanently canceled, then the calculation agent may identify an alternative rate that it determines, in its sole discretion, represents the same or a substantially similar measure or benchmark as CMS10, and the calculation agent may deem that rate (the “successor CMS rate”) to be CMS10. Upon the selection of any successor CMS rate by the calculation agent pursuant to this paragraph, references in this pricing supplement to the original CMS10 will no longer be deemed to refer to the original CMS10 and will be deemed instead to refer to that successor CMS rate for all purposes. In such event, the calculation agent will make such adjustments, if any, to any level of CMS10 that is used for purposes of the notes as it determines are appropriate in the circumstances. Upon any selection by the calculation agent of a successor CMS rate, the calculation agent will cause notice to be furnished to us and

the trustee.

If the calculation and publication of CMS10 is permanently canceled and no successor CMS rate is chosen as described above, then the calculation agent will calculate the level of CMS10 on each subsequent date of determination in good faith and using its reasonable judgment. Such level, as calculated by the calculation agent, will be the relevant rate for CMS10 for all purposes.

Notwithstanding these alternative arrangements, the cancellation of CMS10 may adversely affect interest payments on, and the value of, the notes.

In the opinion of our counsel, Davis Polk & Wardwell LLP, the notes will be treated as “variable rate debt instruments” that provide for a single fixed rate followed by a qualified floating rate (“QFR”) for U.S. federal income tax purposes. Under the Treasury Regulations applicable to variable rate debt instruments, the notes may be treated as issued with original issue discount (“OID”).

In order to determine the amount of qualified stated interest (“QSI”) and OID in respect of the notes, an equivalent fixed rate debt instrument must be constructed. The equivalent fixed rate debt instrument is constructed in the following manner: (i) first, the initial fixed rate is converted to a QFR that would preserve the fair market value of the notes, and (ii) second, each QFR (including the QFR determined under (i) above) is converted to a fixed rate substitute (which will generally be the value of that QFR as of the issue date of the notes). The rules described under “United States Federal Tax Considerations — Tax Consequences to U.S. Holders — Original Issue Discount” in the accompanying prospectus supplement are then applied to the equivalent fixed rate debt instrument for purposes of calculating the amount of OID on the notes. Under these rules, the notes will generally be treated as providing for QSI at a rate equal to the lowest rate of interest in effect at any time under the equivalent fixed rate debt instrument, and any interest in excess of that rate will generally be treated as part of the stated redemption price at maturity and, therefore, as giving rise to OID. Based on the application of these rules to the notes, we will indicate in the final pricing supplement if the notes are issued with OID.

QSI on the notes will generally be taxable to a U.S. Holder (as defined in the accompanying prospectus supplement) as ordinary interest income at the time it accrues or is received in accordance with the U.S. Holder’s method of tax accounting. If the notes are issued with OID, a U.S. Holder will be required to include the OID in income for federal income tax purposes as it accrues, in accordance with a constant-yield method based on a compounding of interest. If the notes are not issued with OID, all stated interest on the notes will be treated as QSI and will be taxable to a U.S. Holder as ordinary interest income at the time it accrues or is received in accordance with the U.S. Holder’s method of tax accounting. If the amount of interest a U.S. Holder receives on the notes in a calendar year is greater than the interest assumed to be paid or accrued under the equivalent fixed rate debt instrument, the excess is treated as additional QSI taxable to the U.S. Holder as ordinary income. Otherwise, any difference will reduce the amount of QSI the U.S. Holder is treated as receiving and will therefore reduce the amount of ordinary income the U.S. Holder is required to take into income.

Upon the sale or other taxable disposition of a note, a U.S. Holder generally will recognize capital gain or loss equal to the difference between the amount realized on the disposition (other than any amount attributable to accrued QSI, which will be treated as a payment of interest) and the U.S. Holder’s tax basis in the note. A U.S. Holder’s tax basis in a note generally will equal the cost of the note to the U.S. Holder, increased by the amounts of OID (if any) previously included in income by the U.S. Holder with respect to the note and reduced by any payments other than QSI received by the U.S. Holder. Such gain or loss generally will be long-term capital gain or loss if the U.S. Holder has held the note for more than one year at the time of disposition.

Under current law Non-U.S. Holders (as defined in the accompanying prospectus supplement) generally will not be subject to U.S. federal withholding or income tax with respect to interest (or OID, if any) paid on and amounts received on the sale, exchange or retirement of the notes if they comply with applicable certification requirements. Special rules apply to Non-U.S. Holders whose income on the notes is effectively connected with the conduct of a U.S. trade or business or who are individuals present in the United States for 183 days or more in a taxable year.

Under their terms, the notes may be assumed by a successor issuer, in which case we will guarantee the successor issuer’s payment obligations under the notes. See “Additional Terms of

the Notes.” We intend to treat such an assumption as not giving rise to a taxable modification of the notes. While our counsel believes this treatment of such an assumption is reasonable under current law and based on the expected circumstances of the assumption, it has not rendered an opinion regarding such treatment in light of the lack of clear authority addressing the consequences of such an assumption. Provided that an assumption of the notes is not a taxable modification, the U.S. federal income tax treatment of the notes would not be affected by the assumption. However, if the IRS were to treat an assumption of the notes as a taxable modification, the timing and character of income recognized with respect to the notes after the assumption could be affected significantly, depending on circumstances at the time of the assumption. Moreover, a U.S. Holder would generally be required to recognize gain (if any) with respect to the notes at the time of the assumption in the same manner as described in the accompanying prospectus supplement in respect of a sale or other taxable disposition of the notes. You should consult your tax adviser regarding the consequences of an assumption of the notes.

The discussions herein and in the accompanying prospectus supplement do not address the consequences to taxpayers subject to special tax accounting rules under Section 451(b) of the Internal Revenue Code of 1986, as amended.

You should read the section entitled “United States Federal Tax Considerations” in the accompanying prospectus supplement. The preceding discussion, when read in combination with that section, constitutes the full opinion of Davis Polk & Wardwell LLP regarding the material U.S. federal tax consequences of owning and disposing of the notes.

You should also consult your tax adviser regarding all aspects of the U.S. federal tax consequences of an investment in the notes and any tax consequences arising under the laws of any state, local or non-U.S. taxing jurisdiction.

CGMI, an affiliate of Citigroup Inc. and the underwriter of the sale of the notes, is acting as principal and will receive an underwriting fee of up to $11.00 for each note sold in this offering (or up to $5.00 for each note sold to fee-based advisory accounts). The actual underwriting fee will be equal to $11.00 for each note sold by CGMI directly to the public and will otherwise be equal to the selling concession provided to selected dealers, as described in this paragraph. From this underwriting fee, CGMI will pay selected dealers not affiliated with CGMI a variable selling concession of up to $11.00 for each note they sell to accounts other than fee-based advisory accounts. CGMI will pay selected dealers not affiliated with CGMI, which may include dealers acting as custodians, a variable selling concession of up to $5.00 for each note they sell to fee-based advisory accounts. Broker-dealers affiliated with CGMI, including Citi International Financial Services, Citigroup Global Markets Singapore Pte. Ltd. and Citigroup Global Markets Asia Limited, will receive a variable selling concession, and financial advisers employed by such affiliated broker-dealers will receive a variable selling concession, of up to $11.00 for each note they sell. CGMI will pay the registered representatives of CGMI a variable selling concession of up to $11.00 for each note they sell directly to the public.

Additionally, it is possible that CGMI and its affiliates may profit from expected hedging activity related to this offering, even if the value of the notes declines. You should refer to “Risk Factors” above and the section “Use of Proceeds and Hedging” in the accompanying prospectus.

The terms and conditions set forth in the Amended and Restated Global Selling Agency Agreement dated April 7, 2017 among Citigroup Inc. and the agents named therein, including CGMI, govern the sale and purchase of the notes.

The notes will not be listed on any securities exchange.

Secondary market sales of securities typically settle two business days after the date on which the parties agree to the sale. Because the issue date for the notes is more than two business days after the pricing date, investors who wish to sell the notes at any time prior to the second business day preceding the issue date will be required to specify an alternative settlement date for the secondary market sale to prevent a failed settlement. Investors should consult their own investment advisers in this regard.

In order to hedge its obligations under the notes, Citigroup Inc. expects to enter into one or more swaps or other derivatives transactions with one or more of its affiliates. You should refer to the sections “Risk Factors—The estimated value of the notes on the pricing date, based on CGMI’s

proprietary pricing models and our internal funding rate, will be less than the issue price,” and the section “Use of Proceeds and Hedging” in the accompanying prospectus.

CGMI is an affiliate of Citigroup Inc. Accordingly, the offering of the notes will conform with the requirements addressing conflicts of interest when distributing the securities of an affiliate set forth in Rule 5121 of the Conduct Rules of the Financial Industry Regulatory Authority, Inc. Client accounts over which Citigroup Inc., its subsidiaries or affiliates of its subsidiaries have investment discretion are not permitted to purchase the notes, either directly or indirectly, without the prior written consent of the client.

See “Plan of Distribution; Conflicts of Interest” in the accompanying prospectus supplement for more information.

Historical CMS10

January 1, 2008 to February 13, 2018