Every December there seems to be considerable confusion as to which tax year applies to year-end income and deductions.

It's a particularly important question this year because--assuming you have no significant changes in your financial situation--your tax rate for 1982 will be about 9 percent lower than for 1981.

The general rule is that income is reportable in the year it is received, and a deduction is properly claimed in the year in which it is paid.

This rule worked fine until some knucklehead invented checks. When you handed over three bear skins and ten beaver pelts in exchange for your trapping supplies for the year, the transaction was completed on the spot, and there wasn't much question about the effective date.

But things are different now, complicated not only by the use of checks but also by credit cards, payments by mail, automatic bank drafts and direct deposits.

It's not that the rule is no longer valid. The problem is in trying to figure out the actual date of payment. Let's look at some typical situations.

In May 1981, in response to a telephone campaign, you pledged $500 to your college alumni society. You mailed them a check on Dec. 28, 1981 which they receive on Jan. 3, 1982. This is a 1981 deduction--not because you made the pledge but because you mailed the check. The date the society receives or cashes it is not relevant.

You visit your dentist on Dec. 15, 1981 and charge the fee on your bank credit card. It shows up on Jan. 25, 1982 statement, which you pay on Feb. 5. Claim the deduction on your 1981 return--the year you charge it on the card, not the year of payment.

You have a pay-by-phone checking account at your bank. On Dec. 29, you call and direct payment of your January mortgage payment, which the bank sends on Dec. 30. But it doesn't appear on the 1981 statement from the mortgagor because it wasn't received until Jan. 6, 1982. Take the interest deduction in 1981--for tax purposes the payment date is the date it is mailed by your bank, as shown on their monthly statement.

On Nov. 5, 1981 you enter a bid for a six-month Treasury bill together with your check for $10,000. On Nov. 20 you get a check for $650 representing the issue discount. Then on May 14, 1982 you get a Treasury check for the face amount of $10,000. The interest is 1982 income--the year the bill matures and is redeemed, not the year in which you get the discount check.

You own 100 shares of XYN Corp. Dividend checks are mailed on Dec. 10; you receive yours on Jan. 4, 1982--rerouted to Arlington, Va., from Arlington, Texas. This is income for 1982--the year you received the check, not the year it is mailed.

If you routinely use the dividend statement (Form 1099DIV) issued by the company, you'll miss this, because their records will include this payment for 1981. You should have your own record of dates of receipt.

Your broker holds your various securities in street name in your account. On Jan. 6, 1982 you get his December statement showing the stock dividends and bond interest received in December. Report this income for 1981--the year it is credited to your account (and therefore available to you) rather than the year you find out through your account statement.

You own mutual fund shares held for you by the sponsor's trustee bank, with automatic reinvestment of dividends. The fund issues a Dec. 31 dividend, which is credited to your account as of that date. This is 1981 income--the year it is added to your account--even if you don't learn about it until some time in January.

Take the same situation, except that the fund mails the quarterly dividend check directly to you--and the Dec. 31 check reaches you on Jan. 6, 1982. Now the dividend is reportable for 1982, the year you receive it.

Next week we'll take a look at the reporting criteria for capital gains and losses. There are a couple of special rules covering the sale of securities that make year-end timing important.