percentage increases over time

Hi. I have a list of over 2000 cities, and I need to determine percentage increases of population over each census (going back to 1860). The first percentage needs to be when the population first exceeds 800 citizens, and the percentage increase after 800 (not the previous census). After that, I need census after census. Unfortunately, since all of these cities exceeded the minimum marker at different census, I'm not sure what I can do to have the first formula be one thing and then everything after that to be a different formula.

To better illustrate what I'm looking for, I tried to mimic a small portion of the table I have.

	A	B	C	D	E
1	City	1990	2000	2010	2020
2	City A	244	438	982	1,001
3	City B	7,000	7,943	7,543	6,894
4	City C	699	850	932	955

So using the above table to find the initial increase over 800 people and then the census over census increase, I think it would look something like this:

First formula: (c2-800)/800
All subsequent formulas: (d2-c2)/c2

Is there a way I could create one formula and fill it down for all cities, or would I have to manually look at each row and type the first formula when the population exceeds 800, and then the second formula for everything after? I hope there is a way I can resolve this simply. Otherwise, it will take days to manually go city by city.

Thanks in advance!