Degree Day Calculator

A plain average-minus-base calculation assumes development happens at a constant rate all day, but real temperature follows a curve that dips below and rises above thresholds at different points during the day. UC IPM's own description of the method is that it "uses a day's minimum and maximum temperatures to produce a sine curve over a 24-hour period, and then estimates degree-days for that day by calculating the area above the threshold and below the curve" — this calculator fits that same sine curve through the day's high-low swing and uses arcsine trigonometry to integrate exactly the portion above your base threshold (and below the upper cutoff), which better matches how development actually accrues on days that cross a threshold partway through.

Many pests stop developing faster once temperatures get too hot, not just too cold, so the calculator caps accumulation at the upper cutoff you set (100°F by default) — the code specifically branches to clip the sine integration when the day's high exceeds that value, capping the contribution rather than letting extreme heat count as extra development.

No — 500 DD per generation is a generic placeholder the calculator uses because generation length varies substantially by species; codling moth, corn earworm, and other pests each have their own published thresholds. Use the generationsEstimate and daysToFirstGen outputs as a rough planning figure only, and substitute your target pest's actual generation-length benchmark from extension-service data for real IPM timing decisions.

Average daily temperature is just the simple midpoint of the day's high and low, with no reference to your pest's biology. Effective temperature above base subtracts your base development threshold from that average (floored at zero), giving a quick read on how much of the day's warmth is actually usable for development — though the calculator's real degree-day figure comes from the fuller sine-curve integration, not this simpler subtraction.