SPGP.US is an ETF that tracks the S&P 500 GARP (Growth at a Reasonable Price) index, so its price is affected by several factors:

GARP Stock Performance: The performance of the GARP stocks within the S&P 500 index directly impacts the ETF's value. Higher performing GARP stocks lead to a higher ETF price.

Index Reconstitution: Changes in the index composition, such as the addition or removal of stocks, can influence the ETF's price, depending on the stocks involved.

Market Sentiment: Overall market sentiment towards growth stocks and value stocks influences investor demand, impacting the ETF's price.

Economic Conditions: Economic factors like interest rates, inflation, and GDP growth can affect the performance of the companies held in the GARP index, thus affecting the ETF's price.

ETF Supply and Demand: Basic supply and demand for the ETF itself can cause price fluctuations independent of the underlying index's performance.

Fund Management Fees: The expense ratio charged by the ETF's management company can slightly reduce the ETF's returns and price over time.