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Opens on Chapter 20’s example: a first quarter of ice-cream sales, $18,000, “on track” for the year.
“On track to”
A fan
A straight line from two early points
A best case on a best case
Enter your numbers, then press Calculate.
How it works
Multiplying a quarter by four ignores the seasons; scaling last year’s total by this year’s share of the same quarters keeps them. A forecast’s error grows roughly with the square root of how far ahead it looks, so the range is center × (1 ± error × √steps). A straight line through two early points keeps their slope forever. Two independent best cases together are as likely as the product of their chances.
From the book, Chapter 20. $18,000 × 4 says $72,000; scaled by last year’s seasons it’s $146,250. 2,500 with an 8% one-step error, nine steps ahead, ranges from 1,900 to 3,100. A straight line through weeks 1 and 4 says 1,589 by week 12. Two 1-in-4 best cases together are 1 in 16. Every chapter and its calculator →
Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12% or 2.5 million. Everything stays in your browser: no sign-up, nothing stored or sent.