Madrigal Pharmaceuticals (MDGL) had the best month in 2018 by a large-cap US stock in May 2018, returning 134.1%.

ASSET	MONTH	% RETURN
Madrigal Pharmaceuticals (MDGL)	May 2018	134.08%
Applied Digital (APLD)	May 2018	133.33%
Applied Digital (APLD)	April 2018	100%
Onto Innovation (ONTO)	May 2018	68.89%
Trade Desk (TTD)	August 2018	68.66%
Trade Desk (TTD)	May 2018	67.02%
Natera (NTRA)	June 2018	60.17%
Madrigal Pharmaceuticals (MDGL)	January 2018	59.95%
Centrais Electricas Brasileiras (EBR)	October 2018	58.53%
AXIA Energia (AXIA)	October 2018	58.52%
Centrais Elétricas Brasileiras SA - Eletrobrás (EBR.B)	October 2018	56.44%
DexCom (DXCM)	August 2018	53.38%
Axon Enterprise (AXON)	May 2018	51.8%
Carvana (CVNA)	August 2018	51.62%
Suzano Papel e Celulose SA ADR (SUZ)	March 2018	50.95%
Bilibili (BILI)	May 2018	49.72%
Wayfair (W)	May 2018	49.02%
Exelixis (EXEL)	November 2018	46.22%
TKO (TKO)	May 2018	45.75%
Centrais Elétricas Brasileiras SA - Eletrobrás (EBR.B)	July 2018	45.66%
Carvana (CVNA)	June 2018	43.99%
Medpace (MEDP)	July 2018	43.52%
Centrais Electricas Brasileiras (EBR)	July 2018	41.36%
AXIA Energia (AXIA)	July 2018	41.35%
Tenet Healthcare (THC)	May 2018	41.16%

Large-cap stocks are treated as having a market cap of $10B+.