These are some of tools that i found useful and can be downloaded free to calculate subnet masks and valid host range and specific classfull or classless adress and also for cidr values. cidr stands for ( Classless inter domain routing )
This software can help you to calculate your data edit no wrong when you are in home and in job but not in ccna exam but if you are too much expert and want to know some basic of networking or ccna then you need to do this trick in your own with pen and paper. If you dont try it home with your own i think this will not increase your skill. So i recommened that first do your own in home then try this in software and you will see that you will learn better then. and also you understand how it works and why subnetting is needed and why cidr is needed.
In here there is a zisko calc software which is very good to convert the decimal number to binary and also hexadecimal and the success of subnetting depends on how you good in binary decimal and in hexadecimal. if you are good with these number system then you will able to any kind of subnetting questions without using software. i already download all of the software that i listed in here and i think this is very useful for me and but also one think that it makes me lazy that i will habit the using of software instead of doing in home.