Distribute a value over a given time period in logarithmic curve

Hi

I am trying to rebuild a business model for the opening of a new building that doesn't require much manual manipulation. There will be different rooms types, and it will be opened in stages. Costs and revenue are dependent on the occupancy, and previously we have started off getting quite a few sales in the first couple of months, then it tapers off as the stock runs out. e.g For the first couple of months, we get 4 sales, then 3 sales, then 2 sales until for the last few of months we are only getting 1 sale per month, until the building is at mature occupancy of 94%.

Previously, we have just manually entered the estimated sales.

I basically want to enter a number of rooms, and a number of months to sell them over, and then forecast how many we will sell each month. To work out the number of months, we would usually say we expect on average 2 sales per month, and then work out how many months that would take. e.g. We have 30 rooms, and plan to sell them at an average rate of 2 per month - so 15 months total.

I have tried googling this, and tried a few different things that don't quite work.

I tried dividing the time period into 3 sections, and saying in the first section 50% of sales would occur, 35% in the section section and 15% in the third section. This kind of worked, but it is a couple of decimal places out, so I had to force the cumulative units not to go over the total units.

I also tried the BetaPer function - but I want the spreadsheet to be easily understood by anyone else who looks at it and the BetaPer function isn't an Excel function. Also, since it graphs a curve, it starts off too slow.

I want it to be like a logarithmic curve, and looked at the logest functions and logarithmic formulas but couldn't work out how to apply them to this problem.

Thanks in advance for you help.