calculator between date periods

Need a windows-based simple program for calculating period length between dates. After entering several date ranges (From / To), the output should be total length in Years, Months and Days. The program should be also able to calculate period length (in Years, Months, Days) between entered period lengths in Years, Months and Days (example: '1 year, 2 months, 5 days' and '2 year, 4 months, 5 days' should calculate 2 years, 6 months and 10 days).