Applied Digital (APLD) had the highest return between 2019 and 2021 by a small-cap US stock, returning 37,647.7%.

ASSET	YEARS	% RETURN
Applied Digital (APLD)	2019-2021	37,647.75%
Accolade (ACCD)	2019-2021	4,692.73%
Digital Turbine (APPS)	2019-2021	3,196.76%
Fulgent Genetics (FLGT)	2019-2021	3,073.19%
Centrus Energy (LEU)	2019-2021	2,943.29%
Aspen Aerogels (ASPN)	2019-2021	2,237.56%
Plug Power (PLUG)	2019-2021	2,176.61%
Atlanticus (ATLC)	2019-2021	1,892.18%
Celldex Therapeutics (CLDX)	2019-2021	1,188%
P10 (PX)	2019-2021	1,154.67%
Skeena Resources (SKE)	2019-2021	1,085.23%
Anavex Life Sciences (AVXL)	2019-2021	1,071.62%
Teekay Tankers (TNK)	2019-2021	1,056.26%
Xpel (XPEL)	2019-2021	1,023.03%
InMode (INMD)	2019-2021	945.63%
eXp World (EXPI)	2019-2021	858.74%
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%
Daqo New Energy Corp ADR (DQ)	2019-2021	776.14%
Clearfield (CLFD)	2019-2021	756.19%
Kornit Digital (KRNT)	2019-2021	720.75%
Arcturus Therapeutics (ARCT)	2019-2021	717%
SolarEdge Technologies (SEDG)	2019-2021	715.37%

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