, how come a K1 form is not due to be given to me until March 15 ?  I have to turn it in with my taxes, ?  I thought Jan 31 was the date ?

K1s are due March 15th, the same day as corporate tax returns.

Your personal income tax is due April 15th or you can get a free extension to Oct 15th if needed.

The return that the K-1 is part of is not due until March 15 so the partnership or small corp doesn't know what your share is yet.

Jan 31 is deadline for W2.  K1's often come much later.

Because it is derived from the creation of a tax return, not just, say, interest on a bank account.