Projected Growth of the SIPP

Initial capital 1st August 2012 = £51,684
15% pa growth = 1.17% per month
For the first 36 months of the SIPP, I paid a monthly contribution of £300.
Since August 2015, my monthly contribution has been £750 a month.
The SIPP projection is based on that £750 monthly contribution continuing, but it may be necessary to cut it, or increase it, in the future.

August 1st to November 1st = 3 months
51,684 plus £300 x 3 = 52,584 @ 1.17% growth / month = 54,440

Year 1 (pe 01Nov13): b/f £55,440 plus £300 x 12; plus 1.17% growth / month = £66,566
Year 2 (pe 01Nov14): b/f £66,566 plus £300 x 12; plus 1.17% growth / month = £80,511
Year 3 (pe 01Nov15): b/f £80,511 plus £300 x 9 and £750 x 3; plus 1.17% growth / month = £98.033
Year 4 (pe 01Nov16): b/f £98,033 plus £750 x 12; plus 1.17% growth / month = £122,638
Year 5 (pe 01Nov17): b/f £122,638 plus £750 x 12; plus 1.17% growth / month = £150,934
Year 6 (pe 01Nov18): b/f £150,934 plus £750 x 12; plus 1.17% growth / month = £183,474
Year 7 (pe 01Nov19): b/f £183,474 plus £750 x 12; plus 1.17% growth / month = £220,895
Year 8 (pe 01Nov20): b/f £220,895 plus £750 x 12; plus 1.17% growth / month = £263,930
Year 9 (pe 01Nov21): b/f £263,930 plus £750 x 12; plus 1.17% growth / month = £313,419
Year 10 (pe 01Nov22): b/f £313,419 plus £750 x 12; plus 1.17% growth / month = £370,332
Year 11 (pe 01Nov23): b/f £370,332 plus £750 x 12; plus 1.17% growth / month = £435,782
Year 12 (pe 01Nov24): b/f £435,782 plus £750 x 12; plus 1.17% growth / month = £511,049
Projected Value of SIPP for 08 November 2024 = £511,049

As a check on my progress, I've put together the "projected growth" of my SIPP.
When I started the SIPP on 1st August 2012, by transferring my managed pension funds into my self-managed SIPP, my target growth was 20% per annum. That was a bit on the optimistic side, and I've reduced the target to 15% pa.

As of today (13th May 2018) I can confirm that I beat my growth target of £150,934 for the 1st November 2017, and I'm well on the way to meeting (and beating) my growth target for 1st November 2018 of £183,474.

At close of business on Friday 11th May 2018, my SIPP had a value of £167,363

Past Performance
Year 1 (pe 01Nov13): Target Value = £66,566   : Actual Value = £67,000
Year 2 (pe 01Nov14): Target Value = £80,511   : Actual Value = £76,000
Year 3 (pe 01Nov15): Target Value = £98.033   : Actual Value = £90,000
Year 4 (pe 01Nov16): Target Value = £122,638 : Actual Value = £113,000
Year 5 (pe 01Nov17): Target Value = £150,934 : Actual Value = £153,000
Year 6 (pe 01Nov18): Target Value = £183,474