In other words, the values cannot exceed 1.0 or be less than -1.0. A correlation of -1.0 indicates a perfect negative correlation, and a correlation of 1.0 indicates a perfect positive correlation.

A simple rolling 25-day correlation between the S&P 500 index and the iShares 20+ Year Treasury Bond TLT exchange-traded fund this week fell to -0.1635, the most negative since June of 2023.