Forecasting Curve Distribution

[Honerun]

Hello,

I am working on a forecasting model and have run into some trouble when trying to extend the X-Axis of a 12-month Curve Distribution to a longer time frame. Given a distribution of 12 percentages (one for each month), how can I spread the 12 months or periods to say 18 months while maintaining the integrity of the curve.

Example:

[TABLE="width: 1235"]
<colgroup><col><col span="4"><col span="2"><col><col><col span="10"></colgroup><tbody>[TR]
[TD]Distribution Amount[/TD]
[TD="colspan: 2"]$1,000,000[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Known Curve[/TD]
[TD]1[/TD]
[TD]2[/TD]
[TD]3[/TD]
[TD]4[/TD]
[TD]5[/TD]
[TD]6[/TD]
[TD]7[/TD]
[TD]8[/TD]
[TD]9[/TD]
[TD]10[/TD]
[TD]11[/TD]
[TD]12[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Bell Curve[/TD]
[TD]1.00%[/TD]
[TD]3.00%[/TD]
[TD]6.00%[/TD]
[TD]8.00%[/TD]
[TD]12.00%[/TD]
[TD]20.00%[/TD]
[TD]20.00%[/TD]
[TD]12.00%[/TD]
[TD]8.00%[/TD]
[TD]6.00%[/TD]
[TD]3.00%[/TD]
[TD]1.00%[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Spend Pattern[/TD]
[TD] 10,000[/TD]
[TD] 30,000[/TD]
[TD] 60,000[/TD]
[TD] 80,000[/TD]
[TD] 120,000[/TD]
[TD] 200,000[/TD]
[TD] 200,000[/TD]
[TD] 120,000[/TD]
[TD] 80,000[/TD]
[TD] 60,000[/TD]
[TD] 30,000[/TD]
[TD] 10,000[/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[TD][/TD]
[/TR]
[TR]
[TD]Adjusted Curve[/TD]
[TD]1[/TD]
[TD]2[/TD]
[TD]3[/TD]
[TD]4[/TD]
[TD]5[/TD]
[TD]6[/TD]
[TD]7[/TD]
[TD]8[/TD]
[TD]9[/TD]
[TD]10[/TD]
[TD]11[/TD]
[TD]12[/TD]
[TD]13[/TD]
[TD]14[/TD]
[TD]15[/TD]
[TD]16[/TD]
[TD]17[/TD]
[TD]18[/TD]
[/TR]
[TR]
[TD]Bell Curve[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[/TR]
[TR]
[TD]Spend Pattern[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[TD]?[/TD]
[/TR]
</tbody>[/TABLE]

 

[sheetspread]

I don't know how to find the pattern exactly but here's a rough guess:

Excel 2010
	A	B	C	D	E	F	G	H	I	J	K	L	M	N	O	P	Q	R	S
6	Known Curve	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18
7	Bell Curve	1.00%	2.00%	3.00%	4.00%	6.00%	7.00%	8.00%	9.00%	10.00%	10.00%	9.00%	8.00%	7.00%	6.00%	4.00%	3.00%	2.00%	1.00%
8	Spend Pattern	10,000	20,000	30,000	40,000	60,000	70,000	80,000	90,000	100,000	100,000	90,000	80,000	70,000	60,000	40,000	30,000	20,000	10,000
Sheet10 (3)