| Document and Entity Information | Feb. 28, 2022 |
| Cover [Abstract] | |
| Amendment Flag | false |
| Entity Central Index Key | 0001865494 |
| Document Type | 8-K |
| Document Period End Date | Feb. 28, 2022 |
| Entity Registrant Name | IO BIOTECH, INC. |
| Entity Incorporation State Country Code | DE |
| Entity File Number | 001-41008 |
| Entity Tax Identification Number | 87-0909276 |
| Entity Address, Address Line One | Ole Maaløes Vej 3 |
| Entity Address, Postal Zip Code | DK-2200 |
| Entity Address, City or Town | Copenhagen N |
| Entity Address, Country | DK |
| City Area Code | +45 |
| Local Phone Number | 7070 2980 |
| Written Communications | false |
| Soliciting Material | false |
| Pre Commencement Tender Offer | false |
| Pre Commencement Issuer Tender Offer | false |
| Security 12b Title | Common Stock, par value $0.001 per share |
| Trading Symbol | IOBT |
| Security Exchange Name | NASDAQ |
| Entity Emerging Growth Company | true |
| Entity Ex Transition Period | false |
