If we don't pay our real estate tax (for our home) in 2021. How much will that affect our refund for 2021?

We do not know if you even have enough itemized deductions to exceed your standard deduction since you have not provided enough information here.   There is a $10000 limit for state and local tax paid that can be used as a deduction on a federal return IF you itemize deductions.   Many people do not have enough itemized deductions to make a difference so the property tax you paid might have no effect at all.

But if you do not pay any property tax in 2021 then you cannot even try to use property tax as a deduction on a 2021 return.   If you pay the tax in 2022 then you can only enter it on a 2022 tax return.   For 2022---you will still be limited to only $10,000 as a federal deduction even if you pay more.

STANDARD DEDUCTION

Many taxpayers are surprised because their itemized deductions are not having the same effect as they did on past tax returns.  The new higher standard deduction and the elimination of certain deductions, as well as the cap on state and local taxes have had a major impact since the new tax laws went into effect beginning with 2018 returns.

Your itemized deductions have to be more than your standard deduction before you will see a change in your tax owed or tax refund.  The deductions you enter do not necessarily count “dollar for dollar;” many of them are subject to meeting  tough thresholds—medical expenses, for example, must meet a threshold that is pretty hard to reach. (Only the amount that is MORE than 7.5% of your AGI counts)   The software program uses all the IRS rules that apply to the expenses you enter, and it tells you if you have enough to use your itemized deductions or if using the standard deduction is more advantageous for you.  Under the new tax laws, some deductions have been capped—there is a $10,000 limit to the itemized deductions for state, local, property and sales taxes.

2021 STANDARD DEDUCTION AMOUNTS

SINGLE $12,550  (65 or older + $1700)

MARRIED FILING SEPARATELY $12,550  (65 or older + $1350)

MARRIED FILING JOINTLY $25,100  (65 or older + $1350 per spouse)

HEAD OF HOUSEHOLD  $18,800  (65 or older +$1700)

Legally Blind + $1350

If you haven't paid any real estate tax for a year, the town is probably getting ready to seize your house and sell it to pay the back taxes. Make sure you pay the tax that you owe in time to avoid losing your home. The effect on your income tax refund is a secondary consideration.

If the total of all your itemized deductions on SCH A 9Which includes property taxes) does not exceed your standard deduction, then weather you pay your real estate taxes in 2021 or not will not make any difference or have any impact on your 2021 tax liability.