Integra Resources (ITRG) had the highest return between 2019 and 2021 by a small-cap US stock, returning 537,400%.

ASSET	YEARS	% RETURN
Integra Resources (ITRG)	2019-2021	537,400%
Fubotv (FUBO)	2019-2021	212,502.74%
Diversified Energy (DEC)	2019-2021	44,900%
DeFi Technologies (DEFT)	2019-2021	6,516.02%
Digital Turbine (APPS)	2019-2021	3,196.76%
Fulgent Genetics (FLGT)	2019-2021	3,073.19%
Lightwave Logic (LWLG)	2019-2021	1,966.67%
Atlanticus (ATLC)	2019-2021	1,892.18%
Aehr Test Systems (AEHR)	2019-2021	1,602.82%
Standard Lithium (SLI)	2019-2021	1,349.04%
HIVE Blockchain Technologies (HIVE)	2019-2021	1,253.85%
Celldex Therapeutics (CLDX)	2019-2021	1,188%
Kodiak Sciences (KOD)	2019-2021	1,100.85%
Anavex Life Sciences (AVXL)	2019-2021	1,071.62%
Teekay Tankers (TNK)	2019-2021	1,056.28%
Xpel (XPEL)	2019-2021	1,023.03%
InMode (INMD)	2019-2021	945.63%
eXp World (EXPI)	2019-2021	858.72%
Perion Network (PERI)	2019-2021	828.57%
Lithium Argentina (LAR)	2019-2021	795.98%
Byrna Technologies (BYRN)	2019-2021	790%
Intellia Therapeutics (NTLA)	2019-2021	785.69%
Envela (ELA)	2019-2021	765.96%
Clearfield (CLFD)	2019-2021	756.19%
IsoEnergy (ISOU)	2019-2021	740.46%

Small-cap stocks are treated as having a market cap between $300M and $2B.