Typically calculators do not allow big numbers because their screens don't have enough pixels to display them. For typical everyday use, regular calculators should handle the numbers you are working with, however, for large numbers, you'll need to use this big number calculator.
What is a Large Number?
There is no specific definition of what a large number is though ten digits or more is a reasonable place to start defining numbers as "big" as they are beyond what most people use on a daily basis.
Having said all that, astronomers, mathematicians, statisticians and people involved in various other fields often use big numbers.