Why , as a retired person and having donated everything I own, mostly new items 12,000 dollars , do I owe on my pension which is not much money?

Charity donations are seldom enough by themselves to get you a bigger refund.   You have to have enough itemized deductions to exceed your standard deduction.

  If you do not have enough deductions to itemize, then your donations will not affect your refund or tax due.  You will just receive the standard deduction.

A charitable donation almost never changes your tax due or refund all by itself.  First, your donation does not count "dollar for dollar"--it is calculated by a percentage based on your tax bracket.  You need a LOT of other itemized deductions like mortgage interest or property taxes, medical expense, etc. to itemize and exceed your standard deduction.

2023 STANDARD DEDUCTION AMOUNTS

SINGLE $13,850  (65 or older/legally blind + $1850)

MARRIED FILING SEPARATELY $13,850  (65 or older/legally blind + $1500)

MARRIED FILING JOINTLY $27,700  (65+/legally blind) )  + $1500 per spouse

HEAD OF HOUSEHOLD  $20,800 (65 or older/blind)  + $1850)

And....

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https://ttlc.intuit.com/questions/4124827-how-do-i-connect-with-a-tax-expert-in-turbotax-live

How much is “low”?   Do you also get Social Security?  

You don't have to file if you only have income under 13,850 but you can file to get back any withholding taken out in W2 boxes 2 or 1099R box 4.

Do you need to file a return?

https://ttlc.intuit.com/community/filing-and-paying-taxes/help/do-i-need-to-file-a-federal-return-this-year/00/25546

In order to benefit from charity donations, your total itemized deductions must be more than the standard deduction, AND your overall taxable income must be more than the standard deduction.  Itemized deductions are property tax, mortgage interest, medical expenses (over a certain threshold) and gifts to charity.  Social security is not taxable unless you have a decent amount of other income.

For example, if you are single, get $2000/month social security and $2000/month as a pension, you should owe about $2500 in taxes with the standard deduction.  If your house is paid off and your medical expenses are low, adding $12,000 in gifts to charity might only save a couple hundred dollars in tax.

Also, you generally can't claim a donation of non-cash items (used clothing, furniture, etc) unless you have your items appraised and get signatures from the charities on a special form that you must file by mail.  We may need more information to help you out with this.