Tandem Diabetes Care, Inc.
MX ˙ BMV ˙ US8753722037
SecurityMX:TNDM / Tandem Diabetes Care, Inc.
InstitutionCitigroup Inc
Latest Disclosed Ownership68,346 shares
Latest Disclosed Value $ 1,310,193
Citigroup Inc ownership in TNDM / Tandem Diabetes Care, Inc.

On May 11, 2026 - Citigroup Inc filed a 13F-HR form disclosing ownership of 68,346 shares of Tandem Diabetes Care, Inc. (MX:TNDM) valued at $1,310,193 USD as of March 31, 2026. The entity filed a previous 13F-HR on February 13, 2026 disclosing 18,368 shares of Tandem Diabetes Care, Inc.. This represents a change in shares of 272.09% during the quarter.

Citigroup Inc has a history of taking positions in derivatives of the underlying security (TNDM) in the form of stock options. The firm currently holds call options representing 0 of underlying shares valued at $0 USD and put options representing 0 of underlying shares valued at $0 USD .

Note: prior versions of this page mistakenly stated that the share values represented the number of options, not the number of underlying shares. For more information on the data backing these reports, please see the SEC document Frequently Asked Questions About Form 13F.

Institutional Ownership: 13F and NPORT Filings

The Security and Class in the table below are shown exactly as filed by the investor. We do our best to track continuity of investments through acquisitions, and this will be reflected in the table as changes in names. In addition to descriptive data, performance of the investment is shown over time. To calculate quarterly performance, we first calculate cost basis of the shares purchased during the quarter, then use that to calculate gross profit. Quarterly return is Gross Profit / Starting Portfolio value.

Note that cost basis is calculated and stored in thousands, so small quarterly changes in shares frequently result in a cost basis of zero.

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Institutional Put/Call Ratios
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In addition to reporting standard equity and debt issues, institutions with more than 100MM assets under management must also disclose their put and call option holdings. Since put options generally indicate negative sentiment, and call options indicate positive sentiment, we can get a sense of the overall institutional sentiment by plotting the ratio of puts to calls. The chart to the right plots the historical put/call ratio for this instrument.

Using Put/Call Ratio as an indicator of investor sentiment overcomes one of the key deficiencies of using total institutional ownership, which is that a significant amount of assets under management are invested passively to track indices. Passively-managed funds do not typically buy options, so the put/call ratio indicator more closely tracks the sentiment of actively-managed funds.

MX:TNDM / Tandem Diabetes Care, Inc. Historical Put/Call Ratio
Disclosed Equity Positions (from 13F/NPORT Filings)
File
Date
Effective
Date
Form Security Class ID Avg Price
Paid (Est)
Reported
Shares
ΔShares ΔShares
(%)
Reported
Value
(x1000)
ΔValue
(%)
Alloc
(%)
ΔAlloc ΔAlloc (%) Cost Basis
(x1000)
Unrealized
Gain/Loss
(x1000)
2026-05-11 2026-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 68,346 49,978 272.09 1,310 225.06 0.0006
2026-02-13 2025-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 18,368 -10,455 -36.27 404 15.47 0.0002
2025-11-10 2025-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 28,823 -58,302 -66.92 350 -78.51 0.0002
2025-08-11 2025-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 87,125 -14,064 -13.90 1,624 -16.20 0.0008
2025-05-12 2025-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 101,189 5,976 6.28 1,939 -43.48 0.0010
2025-02-12 2024-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 95,213 13,183 16.07 3,430 -1.41 0.0020
2024-11-12 2024-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 82,030 -27,644 -25.21 3,479 -21.28 0.0020
2024-08-12 2024-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 109,674 32,831 42.72 4,419 62.37 0.0028
2024-05-10 2024-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 76,843 33,865 78.80 2,721 114.08 0.0018
2024-02-09 2023-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 42,978 13,245 44.55 1,271 106.00 0.0009
2023-12-06 2023-09-30 13F/A-1 TANDEM DIABETES CARE COM NEW 875372203 29,733 -2,759 -8.49 618 -22.58 0.0005
2023-11-09 2023-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 29,733 -2,759 618 0.0002
2023-08-10 2023-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 32,492 2,480 8.26 797 -34.56 0.0005
2023-05-11 2023-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 30,012 20,380 211.59 1,219 181.94 0.0009
2023-02-09 2022-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 9,632 -7,785 -44.70 433 -48.14 0.0003
2022-11-10 2022-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 17,417 -16,296 -48.34 833 -58.27 0.0006
2022-08-10 2022-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 33,713 -1,779 -5.01 1,996 -51.65 0.0015
2022-05-12 2022-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 35,492 -8,998 -20.22 4,128 -38.36 0.0025
2022-02-10 2021-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 44,490 -9,907 -18.21 6,697 3.13 0.0036
2021-11-10 2021-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 54,397 -34,147 -38.57 6,494 -24.70 0.0038
2021-08-10 2021-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 88,544 -28,198 -24.15 8,624 -16.30 0.0052
2021-05-13 2021-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 116,742 46,314 65.76 10,303 52.89 0.0067
2021-02-11 2020-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 70,428 55,200 362.49 6,739 289.99 0.0040
2020-11-12 2020-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 15,228 -17,811 -53.91 1,728 -47.12 0.0011
2020-08-12 2020-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 33,039 -8,337 -20.15 3,268 22.72 0.0026
2020-05-12 2020-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 41,376 16,974 69.56 2,663 83.02 0.0024
2020-02-12 2019-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 24,402 13,716 128.35 1,455 130.59 0.0011
2019-11-08 2019-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 10,686 18 0.17 631 -8.42 0.0005
2019-08-12 2019-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 10,668 -10,181 -48.83 689 -47.96 0.0006
2019-05-13 2019-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 20,849 4,107 24.53 1,324 108.18 0.0013
2019-02-12 2018-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 16,742 10,812 182.33 636 150.39 0.0006
2018-11-13 2018-09-30 13F TANDEM DIABETES CARE COM NEW 875372203 5,930 -1,115 -15.83 254 63.87 0.0002
2018-08-10 2018-06-30 13F TANDEM DIABETES CARE COM NEW 875372203 7,045 6,045 604.50 155 3,000.00 0.0001
2018-05-11 2018-03-31 13F TANDEM DIABETES CARE COM NEW 875372203 1,000 0 0.00 5 150.00 0.0000
2018-02-12 2017-12-31 13F TANDEM DIABETES CARE COM NEW 875372203 1,000 -9,000 -90.00 2 -71.43 0.0000
2017-11-13 2017-09-30 13F TANDEM DIABETES CARE COM 875372104 10,000 0 0.00 7 -12.50 0.0000
2017-08-11 2017-06-30 13F TANDEM DIABETES CARE COM 875372104 10,000 -260 -2.53 8 -33.33 0.0000
2017-05-12 2017-03-31 13F TANDEM DIABETES CARE COM 875372104 10,260 -8,473 -45.23 12 -70.00 0.0000
2017-02-10 2016-12-31 13F TANDEM DIABETES CARE COM 875372104 18,733 17,206 1,126.78 40 233.33 0.0000
2016-11-10 2016-09-30 13F TANDEM DIABETES CARE COM 875372104 1,527 1,527 12 0.0000
2016-08-12 2016-06-30 13F TANDEM DIABETES CARE COM 875372104 0 -13,716 -100.00 0 -100.00
2016-05-13 2016-03-31 13F TANDEM DIABETES CARE COM 875372104 13,716 11,495 517.56 119 357.69 0.0001
2016-02-12 2015-12-31 13F TANDEM DIABETES CARE COM 875372104 2,221 64 2.97 26 36.84 0.0000
2015-11-13 2015-09-30 13F TANDEM DIABETES CARE COM 875372104 2,157 -5,201 -70.68 19 -75.95 0.0000
2015-08-13 2015-06-30 13F TANDEM DIABETES CARE COM 875372104 7,358 5,539 304.51 79 243.48 0.0001
2015-05-14 2015-03-31 13F TANDEM DIABETES CARE COM 875372104 1,819 -530 -22.56 23 -23.33 0.0000
2015-02-17 2014-12-31 13F TANDEM DIABETES CARE COM 875372104 2,349 -220 -8.56 30 -11.76 0.0000
2014-11-14 2014-09-30 13F TANDEM DIABETES CARE COM 875372104 2,569 2,498 3,518.31 34 3,300.00 0.0000
2014-08-14 2014-06-30 13F TANDEM DIABETES CARE COM 875372104 71 -1,347 -94.99 1 -96.77 0.0000
2014-05-15 2014-03-31 13F TANDEM DIABETES CARE COM 875372104 1,418 -3,140 -68.89 31 -73.50 0.0000
2014-02-14 2013-12-31 13F TANDEM DIABETES CARE COM 875372104 4,558 4,558 117 0.0001
Disclosed Call Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share
Price
Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2021-05-13 2021-03-31 13F TANDEM DIABETES CARE COM NEW Call 0 -100.00 0 -100.00 n/a n/a n/a
2021-02-11 2020-12-31 13F TANDEM DIABETES CARE COM NEW Call 16,900 6.29 1,617 -10.42 n/a n/a n/a
2020-11-12 2020-09-30 13F TANDEM DIABETES CARE COM NEW Call 15,900 -53.24 1,805 -46.33 n/a n/a n/a
2020-08-12 2020-06-30 13F TANDEM DIABETES CARE COM NEW Call 34,000 69.15 3,363 160.09 n/a n/a n/a
2020-05-12 2020-03-31 13F TANDEM DIABETES CARE COM NEW Call 20,100 -61.27 1,293 -58.21 n/a n/a n/a
2020-02-12 2019-12-31 13F TANDEM DIABETES CARE COM NEW Call 51,900 19.31 3,094 20.58 n/a n/a n/a
2019-11-08 2019-09-30 13F TANDEM DIABETES CARE COM NEW Call 43,500 -7.45 2,566 -15.37 n/a n/a n/a
2019-08-12 2019-06-30 13F TANDEM DIABETES CARE COM NEW Call 47,000 55.12 3,032 57.59 n/a n/a n/a
2019-05-13 2019-03-31 13F TANDEM DIABETES CARE COM NEW Call 30,300 99.34 1,924 233.45 n/a n/a n/a
2019-02-12 2018-12-31 13F TANDEM DIABETES CARE COM NEW Call 15,200 123.53 577 98.28 n/a n/a n/a
2018-11-13 2018-09-30 13F TANDEM DIABETES CARE COM NEW Call 6,800 291 n/a n/a n/a
Disclosed Put Options
File
Date
Effective
Date
Form Security Class ID Opt Avg Share Price Shares ΔShares
(%)
Value
(x1000)
ΔValue
(%)
Prior Allocation
(%)
Allocation
(%)
ΔAllocation
(%)
Cost Basis
(x1000)
Profit
(x1000)
Return
(%)
2021-05-13 2021-03-31 13F TANDEM DIABETES CARE COM NEW Put 0 -100.00 0 -100.00 n/a n/a n/a
2021-02-11 2020-12-31 13F TANDEM DIABETES CARE COM NEW Put 39,300 4.52 3,760 -11.90 n/a n/a n/a
2020-11-12 2020-09-30 13F TANDEM DIABETES CARE COM NEW Put 37,600 -40.60 4,268 -31.84 n/a n/a n/a
2020-08-12 2020-06-30 13F TANDEM DIABETES CARE COM NEW Put 63,300 29.71 6,262 99.43 n/a n/a n/a
2020-05-12 2020-03-31 13F TANDEM DIABETES CARE COM NEW Put 48,800 17.87 3,140 27.23 n/a n/a n/a
2020-02-12 2019-12-31 13F TANDEM DIABETES CARE COM NEW Put 41,400 8.38 2,468 9.54 n/a n/a n/a
2019-11-08 2019-09-30 13F TANDEM DIABETES CARE COM NEW Put 38,200 76.04 2,253 60.93 n/a n/a n/a
2019-08-12 2019-06-30 13F TANDEM DIABETES CARE COM NEW Put 21,700 59.56 1,400 62.04 n/a n/a n/a
2019-05-13 2019-03-31 13F TANDEM DIABETES CARE COM NEW Put 13,600 -8.72 864 52.65 n/a n/a n/a
2019-02-12 2018-12-31 13F TANDEM DIABETES CARE COM NEW Put 14,900 396.67 566 338.76 n/a n/a n/a
2018-11-13 2018-09-30 13F TANDEM DIABETES CARE COM NEW Put 3,000 129 n/a n/a n/a
Legend
Shares
The total number of shares held by the institution at the end of the reporting period (the effective date). This is provided in the filing.
Value
The total value of the shares as of the effective date. This is provided in the filing.
Avg. Share Price
The weighted average share price of the shares held by the institution. We use FIFO accounting to determine this price
Class
This is the security class as indicated by the filer. There are a variety of values for this field. Common values include "EC" = equity common, "EP" - equity preferred
Allocation (%)
The percent of the institution's portfolio that this position represents. This is provided in NPORT filings. For 13F filings, we calculate it.
Change in Allocation
The change in allocation from the prior reporting period. This is calculated as current allocation - prior allocation.
Change in Allocation (%)
The percent change in allocation from the prior reporting period. This is calculated as (current allocation - prior allocation) / prior allocation.
Cost Basis
The total cost of the shares held. This is calculated as reported shares * avg. share price
Unrealized Gain/Loss
This is the market value of the position as of the effective date minus the cost basis.