weeks-from-now

You may want to know date of 6 weeks from now:

$ weeks-from-now 6
2017-09-19

You may even want to know date of 3 weeks ago:

$ weeks-from-now 3 --past
2017-07-18

Following is the most easy way to install the tool (assuming you have the Rust toolchain installed):

cargo install weeks-from-now

NOTE: minimum required rustc is v1.74, due to clap (a direct dependency).