How do I modify a recipe when I add or subtract an ingredient? For the most part, we take the same percentage from the water in the heated water phase. A few examples...
You add 10% aloe vera to a lotion. Take 10% away from the water amount.
You add 2% panthenol to a shampoo. Remove 2% from the water amount.
You add 2% panthenol, 5% liquid green tea extract, 2% hydrolyzed oat protein, 0.5% polyquat 44 to a conditioner. Remove 9.5% from the water amount.
If you use 20% lavender hydrosol, 10% aloe vera, 10% chamomile hydrosol, 0.5% powdered grapeseed extract, 0.5% powdered honeysuckle extract, 0.5% allantoin, 0.5% MSM, 2% niacinamide, and 2% salicylic acid, you would remove 44% from the water phase.
I realize many of the ingredients in this last example are powdered, but that doesn't change that we remove the additions from the water amount. This will change the consistency of the product - you've added 6% powders and removed 6% water, which will likely make it thicker - but you've kept the recipe relatively the same.
It doesn't matter if your added ingredient is in the heated water, heated oil, or cool down phase. You still remove the addition from the water amount.
A final example: You add 5% oils to a lotion. Remove 5% from the water amount - AND recalculate your oil phase. You have 5% more oil in your product, so you must recalculate your emulsifier. For Polawax, you would add 1.25% more, and remove a total of 6.25% from your water phase. (If you are using an emulsifier other than Polawax, you'll have to recalculate according to the manufacturer's suggested usage rates.) For the most part, it's easier to substitute one oil for another rather than doing all the recalculating, but I encourage you to add more oils and recalculate as it is one of the first steps to making your own recipes!
If you want to know more about modifying lotions and how to add or subtract ingredients, I wrote about it fairly extensively in the learning to formulate series few months ago. I'm writing this on my iPhone so I can't link, but if you can't wait for me to update this post tomorrow, scroll down and look for formulating in the labels. It's one of the first few posts.