Business & farm

Generally, even though you "paid" for your inventory, you can't deduct the cost of year-end inventory until it's sold.  For 2018, the beginning year of your business, opening inventory would be $0.  However, you should have reported EOY inventory...thus reducing your COS for 2018.  BOY for 2019 would be the same number as the EOY for 2018.

Changing the way you do it for 2019 from 2018, would be a change in accounting method.  I would suggest amending 2018 to reflect the inventory you had on hand at the end of 2018.  Then enter that number as BOY inventory for 2019.  Also, you should have the EOY inventory for 2019.

General Formula:

BOY Inventory                 $xx,xxx

Purchases                           xx,xxx

Available goods             -----------

   for sale                          $ xx,xxx

less:

EOY inventory              ($xx,xxx)

                                        --------------

COS                             $xx,xxxx

For more guidance, please review IRS Publication 334, Tax Guide for Small Business

https://www.irs.gov/pub/irs-pdf/p334.pdf

There are different methods of valuing ending inventory.  Common methods are cost, cost or market, whichever is lower, LIFO (Last in First Out a detailed method), retail method, etc.

If you meet the small business exception, you don't have to inventory per se.  BUT, you must then treat the inventory as non-incidental material or supplies.  Which still means you can't deduct the goods until they are basically sold or consumed.  Page 15 of Pub 334.