Absolutely @Jennifer - in theory it's balanced. Unless you have completed some interesting mathematical calculations you don't know if the minerals and vitamins from each food have remained in balance as different amounts are frequently quoted on different foods. Most of what we calculate relates to calories

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This just doesn't make sense! There are no calculations to be made. With kibble, each mouthful of food is exactly the same which means that every piece of kibble is balanced (however that is defined for that particular food) with the correct percentage of each and every nutrient. If your dog needs one cup a day, he is getting a balanced diet. If he needs three cups a day, he is getting a balanced diet. That's that.
If the thing you are mixing it with is also balanced, then the same applies. When feeding raw or home made, obviously not every mouthful is the same, so you need to make sure that, over what you do feed, you are getting the right balance. But as long as you do that, there are no further calculations to make by mixing one balanced source with another. If both are balanced, then the whole will be balanced, whatever proportions you choose to feed them in. If either one of them is unbalanced, then the nutritional profile as a whole will be unbalanced, but it makes no sense at all to say that mixing balanced foods from different manufacturers or mixing a complete kibble with any other balanced food source will create an imbalanced diet.
Feed a balanced raw diet and chuck in two pieces of kibble => balanced diet.
Feed kibble and chuck in a spoonful of premade raw* => balanced diet.
Move that line of how much of each food you're giving and it makes no difference. It will always be a balanced diet.
* I say premade raw here only because it's difficult to get a balanced raw diet in a spoon-sized amount without it being minced up!
The only thing you will have to figure out is how much volume or weight of each you need to feed, because they will have different caloric densities, meaning that one cup of one type of food has more calories than the same volume of the other food. I don't work out caloric values for the food I eat, nor for the food my dogs eat. Not do I weigh or measure it - that doesn't make sense as their activity levels vary day by day and week by week, as does the number of training treats they get. I just feed them and if they're looking a bit porky, I cut down their food and if they're looking a bit lean, I increase it.
reminded me of something my vet told me a couple of years ago about feeding raw or kibble. On paper feeding half and half is a balanced diet but it's the dogs ability to digest both types of food that determines whether it is balanced. A dog fed completely raw food has a much more acidic (I think I've got that the right way around) digestive system than one fed on kibble and consequently wouldn't fully digest kibble and vice versa. The problem feeding half and half is can a dogs digestive system adapt to fully digest both types of food.
This has no basis in evidence. Here is a very interesting article on it which, I think, does a very good job of saying that it's really unlikely there is a problem mixing.
Gastric pH in raw & kibble fed dogs
TL;DR
...the claim that kibble fed dogs actually have neutral or alkaline gastric pH values is completely unsubstantiated and verifiably false. An alkaline or neutral gastric pH would not be able to digest raw OR kibble, and would result in severe malnutrition.
What this means is that the significance of this difference in gastric pH between raw and kibble fed dogs has been highly exaggerated in order to fit some raw feeders’ “all or nothing” agendas.
Note this is from a site which is aimed at raw feeders!!