Find growth from dates group by months
AS I explained on my previous answer you can use a variable to store last entry value.

In this case you need to count entries grouped by year and month.

SELECT Year, Month, Entry, 
       IF(@last_entry = 0, 0, ((entry - @last_entry) / entry) * 100) "Growth Rate",
       @last_entry := entry                  
FROM
      (SELECT @last_entry := 0) x,
      (SELECT YEAR(leadDate) Year, MONTH(leadDate) Month, COUNT(*) Entry
       FROM   Lead
       GROUP BY 1,2) y;


This is the result:

| Year | Month | Entry | Growth Rate      |
|------|-------|-------|------------------|
| 2016 | 6     | 1     | 0                |
| 2017 | 3     | 1     | 0                |
| 2017 | 4     | 1     | 0                |
| 2017 | 5     | 2     | 50               |
| 2017 | 6     | 9     | 77,7777777777778 |


Rextester here