Start-and-End Date Explorer: How the Window Changes the Story

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Opens on Chapter 11’s example: 24 months of riders on Millbrook’s bike lane: “up 40%” and “down 15%” from the same record.

Values, in order one per period, comma-separated

Start at period 1 = the first

End at period

Periods in a year for year-over-year

Load another example from the book

Enter your numbers, then press Calculate.

How it works

The change over a window is (end − start) ÷ start. Comparing with the same period a year earlier takes the seasons out. With n values there are n × (n − 1) ÷ 2 possible windows; counting how many rise and how many fall shows whether the story depends on the choice.

From the book, Chapter 11. January to May is up 40%; the peak to May is down 15%; May against the May before is up 8.2%; from the low it’s up 67%. Of 276 windows, 135 rise, 139 fall and 2 are flat, from up 96% to down 45%. 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.