Brewing method, bean/leaf type, serving size, and brand all affect caffeine content significantly. Check the specific product if you want an accurate number — the values in this tool are just typical ranges.
Smoking can roughly halve caffeine's half-life; pregnancy, certain medications, and some liver conditions can roughly double or triple it. If you know your situation affects it, adjust the number accordingly.
Not exactly — this just tracks the amount of caffeine remaining in your bloodstream mathematically. Perceived alertness and actual sleep impact can differ from the raw remaining-amount curve.