I am a little confused by your terminology and example.
First, if the "initial sales figure" is the initial __monthly__ sales, note
that 6 times $300 is $1800. Ergo, no increase(!) is needed to achieve
Second, by "linear percentage growth", I assume you mean non-compounding.
But "percentage [...] increase every period" sounds like a compounded growth
rate. Which do you really mean?
----- (linear growth)
Suppose the initial (average) monthly sales is $300, and you want the
cumulative sales over 6 months to be $2500 -- usually something larger than
$300 times 6 ($1800).
More generally, suppose A1 contains the initial (average) monthly sales, A2
contains the required cumulative sales, and A3 contains the number of
Then the "linear growth" (not the linear percentage growth) can be computed
as follows (in A4):
You can confirm that result by entering =ROUND($A$1+$A$4*ROWS($B$1:B1),2)
into B1 and copying B1 down through A3 rows (e.g. through B6). Then
=SUM(B1:B6) should be about A2.
It might be off by as much as $0.01*A3 due to rounding. The use of
$A$4*ROWS($B$1:B1) instead of incremental addition to rounded figures is
intended to minimize rounding error.
Also note that A4 might be negative if A2 is less than A1*A3, as it is with
your example. That is, A4 might represent an incremental decrease as well
as an incremental increase.
You might express the linear growth as a percentage of initial (average)
monthly sales as follows:
formatted as Percentage. But I think it is ambiguous and it might be
confusing to say that "11.11% percentage increase every month". I would
simply say "increase by $33.33 every month".
----- (compounded growth rate)
On the other hand, if you actually want the compounded growth rate -- the
formatted as Percentage. See the example above for the explanation for the
expected contents of A1, A2 and A3.
You can confirm that result by entering
=ROUND($A$1*(1+$A$4)^ROWS($B$1:B1),2) into B1 and copying B1 down through A3
rows (e.g. through B6). Then =SUM(B1:B6) should be about A2.
Again, it might be off by some relatively small amount due to rounding. The
use of (1+$A$4)^ROWS($B$1:B1) instead of incremental multiplication of
rounded figures is intended to minimize rounding error.