Is Delta always positive?

No, delta is not always positive, and it can be positive, negative, or zero depending on what you are measuring and in which field you are using it. In general mathematics and science, delta represents change calculated as final minus initial. If the final value is larger than the initial value, delta is positive, indicating an increase. If the final value is smaller, delta is negative, indicating a decrease. If there is no change, delta is zero. For example, if temperature goes from 20 to 25 degrees, delta is +5, positive. If it goes from 25 to 20, delta is -5, negative. In finance and options trading, delta is definitely not always positive. Call options have positive delta ranging from 0 to +1, meaning they go up when the stock goes up. Put options have negative delta ranging from -1 to 0, meaning they go up when the stock goes down. A -0.50 delta put profits when the stock falls. In chemistry, delta H can be negative for exothermic reactions that release heat, or positive for endothermic reactions that absorb heat. In business, delta can be negative if you are under budget or under target. So delta is a neutral term for change, and its sign tells you the direction of that change. It is positive for increase and same-direction movement, negative for decrease and inverse movement.