Company: MIRM
Filing Date: 2025-08-12
Form Type: S-3ASR
Source: 0001193125-25-178937
Chunk: 47

Company: Mirum Pharmaceuticals, Inc.
Filing Date: 2025-08-12
Form: S-3ASR
Chunk 47
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 page S-10 of this prospectus supplement. |

| Risk factors | Investing in our common stock involves a high degree of risk. Please read the information contained in and incorporated by reference under the heading “Risk Factors” beginning on page S-6 of this prospectus supplement, and under similar headings in the other documents that are filed after the date hereof and incorporated by reference into this prospectus supplement, before deciding whether to 
 invest in our common stock.                                                                                                                                                                                                                                                                                                                                                                                 |

| Nasdaq Global Market symbol | “MIRM” |

The number of shares of our common stock to be outstanding after this offering set forth above is based on 50,058,392 shares of our common stock outstanding as of June 30, 2025 and excludes:

| • |     | 10,585,707 shares of our common stock issuable upon the exercise of stock options outstanding as of June 30, 
 2025, at a weighted-average exercise price of $23.15 per share;                                              |

| • |     | 1,538,186 shares of our common stock issuable upon the vesting and settlement of restricted stock units 
 outstanding as of June 30, 2025;                                                                        |

| • |     | 353,743 shares of our common stock issuable upon the vesting and settlement of performance stock units 
 outstanding as of June 30, 2025;                                                                       |

| • |     | up to 9,963,963 shares of our common stock issuable upon the conversion of convertible notes outstanding as of 
 June 30, 2025;                                                                                                 |

| • |     | 2,240,571 shares of our common stock reserved for future issuance under our 2019 Equity Incentive Plan, or 2019 
 Plan, as of June 30, 2025, as well as any automatic annual increases in the number of                           |

S-4

| shares of common stock reserved for issuance under our 2019 Plan and any shares underlying outstanding stock awards granted under our 2018 Equity Incentive Plan, or 2018 Plan, that expire or are 
 repurchased, forfeited, cancelled or withheld;                                                                                                                                                     |

| • |     | 1,806,244 shares of our common stock reserved for issuance under our 2019 Employee Stock Purchase Plan, or ESPP,                                        
 as of June 30, 2025, as well as any automatic annual increases in the number of shares of common stock reserved for