Hiya Rat2
If your buying 100mg, and using 18% in your recipes, cut it in half.
I say half because if you make a recipe using a flavor percentage over 15%, it won't work out below a 70PG/30VG mix.
So if you like more VG, you need room to play with it in the recipe.
I'm assuming your buying you nic in 100% PG.
If you only use 5-10% flavoring, then you can cut it to 36mg.
But, it's easier math wise to just split it in half.
I cut mine to 3 times my desired end percentage.
Most of the recipes I make, I'm using 17- 20% flavoring (don't ask)
If I don't keep my base mg high, I won't have room to dilute it.
It's easier to add more PG or VG at the time of making the recipe.
Otherwise, I have to stay in the 80PG/20VG range, and I like room to alter the recipe.
My base mg is in 100% PG, and then I dilute with VG (and more PG if needed.)
It all depends on:
1- what your base is composed of
2- how much your going to dilute it
3- what you use to dilute
But if I were you, I'd cut my base to at least double what you want it to come out at (you 18%)
18+18 is 36, so I'd just cut it in half to 50mg. That way you have some leeway
It's pretty much a guessing game, ...and getting it to work out on e-juice me up.
If you order your base nic in a combo of PG and VG, You've lost me ...
I'm a KISS ( Keep It Simple Stupid ) person.
Have fun