Some flavors are stronger than others. TFA flavors are often used at 5-15% as single flavors, and I've seen recipes with several flavors totaling 30% or more altogether.
Yeah, you might have a hard time with a calculator, with what you've got. You're going to have to "trick" it into giving you recipes that only take nic base and flavoring, by asking it for only very specific things some of which you'll have to work out by hand. Say you want to make a recipe with 14% flavoring (say for example, 6% Strawberry, and 8% Vanilla Bean Ice Cream*.) You plug in your recipe and your nic base (12mg 100VG 0PG) into the calculator. It asks what your target strength/ratio are. You tell it something like 6mg, 50VG 50 PG. It's going to tell you to add PG. Well you don't have any PG. How about you tell it 100VG 0PG as your target. Well, that's not going to work either, since the flavors have some PG in them, and most calculators just treat them as PG. If you ask it for 100% VG, it's going to tell you to put negative PG in the mix. How you gonna do that? So you know that since you have 14% flavoring, you have to have at least 14% PG in the mix. And you don't want to add any MORE PG, so you want to have EXACTLY 14%. Okay, so you ask it for a target of 6mg 86VG 14PG. Now it tells you to add VG. Because in order to cut your 12mg down to 6, you need to dilute it by half, or 50%. But your mix only calls for 14% flavors, so with 14% flavor and 50% nic base, you still need another 36% to fill it out. So the calculator is asking for straight VG (since you told it not to use any more PG than what was already in the flavors) to fill that 36%. Okay, so what happens if you dilute 12mg by 14%? 86% of 12 is 0.86 * 12 = 10.32. Okay, so if you take your 12mg nic base, and add ONLY 14% flavors to it, then you'll end up with 86%VG, 14%PG, and whatever 86% of 12mg is, which is 10.32. So finally, if you ask the calculator for a target of 10.32mg, 86%VG, and 14%PG, and you enter the recipe as 6% Strawberry and 8% VBIC, then it will give you a recipe with only nic base and flavorings. But at this point it might have been easier just to pull out some scratch paper and do it the old-fashioned way. 6% of 30ml, for example, is 1.8ml Strawberry flavor. 8% is 2.4ml VBIC. Add those together (4.2ml) and subtract from 30 (25.8) gives you the remaining amount of nic base you'll need. The nic strength, since you didn't buy any plain PG or VG, you don't get to decide, it just "is what it is" depending on how much flavor you add. It'll be something less than 12mg, how much less depends on how much flavor you used. In this case, we already learned earlier that it's 10.32 mg/ml since 14% flavor means 86% nic base, and so 86% of 12mg.
*edit: not my recipe, but one I found on .................... that I tried recently, simple to make and came out tasting pretty good even with only two flavors.
*edit edit: we can't say e-hyphen-liquid-hyphen-recipes(dot)com here? Bitter admin rivalry? What'd he do, kick your dog? Kiss your girl? Kick your girl and kiss your dog?