Upstart Holdings (UPST) had the highest return in March 2021 by a mid-cap US stock, returning 93%.

ASSET	MONTH	% RETURN
Upstart Holdings (UPST)	March 2021	92.96%
Advantage Solutions (ADVWW)	March 2021	78.33%
Tecnoglass (TGLS)	March 2021	57.91%
United States Steel (X)	March 2021	53.94%
Cleveland-Cliffs (CLF)	March 2021	43.64%
Marathon Digital (MARA)	March 2021	40.33%
Vizio (VZIO)	March 2021	38.57%
LGI Homes (LGIH)	March 2021	34.98%
QXO (QXO)	March 2021	31.72%
Acuity Brands (AYI)	March 2021	30.94%
Uranium Energy (UEC)	March 2021	30.59%
Fluor (FLR)	March 2021	30.38%
Telephone and Data Systems (TDS)	March 2021	27.52%
Alcoa (AA)	March 2021	26.57%
Central Garden & Pet (CENT)	March 2021	26.14%
Federal Agricultural Mortgage (AGM.A)	March 2021	25.16%
United States Cellular (USM)	March 2021	23.87%
Avis Budget (CAR)	March 2021	23.64%
Central Garden & Pet Company A (CENTA)	March 2021	23.4%
Box (BOX)	March 2021	23.37%
Braskem SA Class A (BAK)	March 2021	23.01%
Abercrombie & Fitch (ANF)	March 2021	22.06%
Ufp Industries (UFPI)	March 2021	22.03%
AutoNation (AN)	March 2021	21.89%
Stride (LRN)	March 2021	21.61%

Mid-cap stocks are treated as having a market cap between $2B and $10B.