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# S-Curve (Logistic Function) Calculator

You want to forecast a growth function that is bound to hit a limit (S-Curve or Logistic function) and you can estimate the function's 3 key parameters. Just enter the requested data and you'll have an immediate answer.
[areppim's S-curve solution with 1 parameter estimate gets you a fast and easy first pass.]

Start time (period or year)

End time (period or year)

Value at the beginning of the period

Value at the end of the period

#### Parameter estimates

Saturation (upper limit)

Midpoint (period or year)

Time to grow from 10% to 90%

#### Time Span

Forecast horizon (period or year)

#### Instructions

1. Known data :
• enter the start and the end of the period for which you have data in the text fields next to "Start time (period or year)" and "End time (period or year)". Entries should be natural numbers not longer than 4 digits.
• enter the known values at the beginning and at the end of the period in the text fields next to "Value at the beginning of the period" and "Value at the end of the period".
2. Forecast :
• enter the three required parameter estimates (arrived at by trial and error or by a procedure [e.g. Monte Carlo, bayesian parameter estimation] that minimizes the deviations between actual and forecast data points):
1. saturation : your's own or the expert's upper limit estimate.
2. midpoint (period or year) : the inflection point where exponential growth stops and exponential decay begins.
3. time to grow from 10% to 90%.
• enter the horizon time for your forecast in the text field next to "Forecast horizon (period or year)". Entry should be a natural number not longer than 4 digits.
3. To correct an entry, click the Reset button.

You may elect to walk through the following S-Curve example.