Fever Defervescence Calculator

How it is calculated

Two readings in °C and the hours between them give a straight-line rate: total drop = start − now and rate = drop ÷ hours (°C per hour). If the current reading is above 37 °C and the rate is positive, the projected time to normal is (now − 37) ÷ rate hours. If the current reading is already 37 °C or below, the projection shows 0 h. If the temperature is flat or rising, the projection shows a dash because it never reaches 37 °C at that pace, and the rate and drop are negative or zero. Results are rounded to two decimals. Hours must be above zero and both temperatures must lie between 30 and 45 °C; anything outside that range, which includes Fahrenheit readings, gives no result. The target of 37 °C is fixed, and the projection assumes the same drop every hour.

Common mistakes

• Typing Fahrenheit readings such as 102 and 100. The tool expects °C and rejects anything above 45, so it shows no result; convert to °C first.
• Entering the hours since the fever peaked rather than the hours between the two readings. The rate then describes the wrong interval.
• Swapping the two readings. The first field is the earlier, usually higher, value. A later reading that is higher, say 38 then 39 over 3 hours, gives a rate of -0.33 °C/h and a dash for time to normal.
• Treating the projected time as a forecast. It extends a straight line from two points, and real fevers often fall in steps or level off.
• Mixing measurement sites, for example an ear reading first and an oral reading second. Part of the apparent drop is then the difference between methods.