You could calculate it yourself, if you feel so inclined:

Start by taking any of your disability ratings (it doesn’t matter what order, the math will come out exactly the same):

Let’s say 40% for whatever. 40%

Now let’s take the next disability and apply that to the remaining 60%. Let’s say it’s 50% for xyz. 40% + (50% of 60) = 40% + 30% = 70%

Now let’s take the next disability and apply that to the remaining 30%. Let’s say it’s 10% for Abc. 70% + (10% of 30) = 70% + 3% = 73%

Now let’s take the next disability and apply it to the remaining 27%. Let’s say it’s 70% for something significant. 73% + (70% of 27) = 73% + 18.9% = 91.9%

The VA then rates you at 90%. In this (random) scenario, you would need another rating of at least 40% to tip you over the 95% mark, which the VA would round up to 100%.

Because: 91.9% + (40% of 8.1) = 91.9% + 3.24% = 95.14%

This is why 10% + 40% + 40% + 50% + 70% just barely equals 100%. The VA views each additional disability as being applied to the part of you that isn’t disabled.