Hi, Jo.
My guess is that the excess is from unrecorded income, which should have been reported as dividends in some prior year(s) - since a Money Market Fund was treated like a special kind of corporation for tax purposes. The fund collected interest and made profits on short-term sales of notes and other interest-bearing assets. While the fund might realize interest and capital gains, what they passed through to account-holders was taxed as dividends.
The income should have been reported as income in the prior years, of course. If the income was intentionally omitted from your return, the IRS might allege fraud, which would let them assess tax "at any time". But if the omission was unintentional and the returns were filed more than three years ago, the statute of limitations has probably run by now and it's too late to correct the omission, even if you want to.
You might have a freebie. Or maybe there was no omission at all, just sloppy bookkeeping. So just (in accountant-speak) debit Cash for the amount of the check, credit Fidelity for the balance in the account and credit Miscellaneous Income for the excess.
One small quibble: There is a difference between a Money Market ACCOUNT, which pays INTEREST at a rate based on the "money market", and a Money Market FUND, which buys and sells short-term assets and pays DIVIDENDS, as I said above. In most cases, the effect on your return and your tax bill would be identical except for which form you would use to report it, and the time limitation would be the same either way.
Remember, Jo: I've been retired for over 20 years and some rules may have changed, so check with your own CPA to be sure.
RC
-- -- R. C. White, CPA San Marcos, TX (Retired. No longer licensed to practice public accounting.) snipped-for-privacy@grandecom.net Microsoft Windows MVP (2002-2010) (Using Quicken Deluxe 2014 R 7 and Windows Live Mail in Win8.1 x64)
I've closed out my Fidelity account, getting a check for the cash which was in a linked Money Market account . Somewhere across the years I introduced some errors into it and Quicken says I have about $300 more than Fidelity had recorded, and I'm inclined to believe them. I have not been using this account for investing for years and looking back on it, I wasn't doing any kind of reconciliations so the error could have happened many, many years ago and I will never find it. What kind of simple adjusting entry can I make in Quicken to wipe out the discrepancy in the Money Mkt Account?