excel formula

between two dates that are a year apart like 14th jan2023 to 14th jan2024-assuming this duration is divided btw weeks, so first week will be 14th to 21st. If i input a date 15th jan in my function it should return 21st, however if it is 14th jan that i input it should return 14th. but for 15th,16,17,18,19, 20 it should return 21st