I have about $4,000 in investment expense with Fidelty from them managing my 401k at a 1% charge. Can i write it off?

IRA and 401k maintenance fees can't be deducted if they are paid by the tax deferred account. Instead, they would reduce the amount in the IRA or 401k, which would reduce the amount subject to tax when finally distributed.

For tax years 2018 through 2025, due to the Tax Cuts and Jobs Act (TCJA), you can no longer deduct retirement or investment maintenance/management fees as a miscellaneous itemized deduction. 

If you're amending your 2017 or earlier income tax return, to enter investment fees and expenses: 

1. Open your return if it’s not already open.
2. Search for investment expenses and then select the "Jump to" link in the search results.
3. Continue with the onscreen interview until complete.

Related information:

• Can I claim tax prep fees as a deduction?
• Can I itemize my deductions?
• What is Schedule A?

[Edited 3-11-2020|11:18 am PST]

The hidden fee in a mutual fund , like the 1% management fee & expenses, is never deductible, because it is reflected in the NAV price and eventually reduces the taxable amount distributed.