"No one really knows exactly what formula to use. Deca is likely the harshest
steroid on your HPTA, therefore it is wise to extend PCT timing. The 2 week difference between the cycles mentioned (14 weeks vs 16 weeks) is not an impactful amount of time. 10 weeks vs. 18 weeks is a big difference and would call for a more aggressive PCT.
We have to remember that all of this is very individualistic and cannot be quantified with a formula, but based on history and how drugs interact with the majority, you can make judgment calls for the betterment of recovery. In other words, you can assume you'll be OK, or you can take some extra measure to better your chances at recovery.
The best method in my opinion for the common cycles with Deca (12 to 14 weeks), is to extend PCT for 2 additional weeks. You can use
Nolvadex and drop clomiphene after the 4th week. Then you would wait 6 to 8 weeks and confirm recovery with blood work. If the results fail, run another PCT for 4 weeks and retest. If you're good, you're good."