401k contribution for 2018 before tax filing

I had a job change last year and end up contributing only $14,500 to my 401k. The internet says I can contribute additional $4,000 before April 15th to reduce my taxes (I owe around $9,000). However, I cannot figure out how to do it (can't find anything on hrweb and fidelity.com) or how to report it using TurboTax or Credit Karma. Has anyone done it? If yes - how, and did you get the employer match? Thank you in advance!

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Juniper sixpack Mar 12, 2019

401k contributions has to be through payroll deduction. You can’t contribute additional 4K now. But, depending upon your income, you may be eligible to contribute to IRA upto 5.5k which will help you in tax deductions.

Netflix Thats_It Mar 12, 2019

Because 401K is Pre-tax contribution, you can’t add to it post-tax. That’s why it’s taken out of payroll to reduce your income at the time of earnings. You’ll need to look at an IRA.

General Motors agmV57 Mar 12, 2019

You can contribute after tax money to a 401k if you want - you just select "Roth" contribution. Of course, this doesn't really help you during tax time now, but it will be great in the future!

Microsoft LUVn81 OP Mar 12, 2019

There are some murky articles that say "Ask your employer payroll department to do the contribution from your next paycheck and to designate it for 2018", that's why I got hopes. I don't have an IRA only a employer sponsored 401k and don't know whether I can open one now and make a 2018 contribution. I am itemizing and thought I can beat the new standard deduction, not knowing sales plus property taxes are capped at 10k

Microsoft LUVn81 OP Mar 12, 2019

Yeah, did some reading - my income is too high to deduct any piece of an IRA contribution and on top both me and my wife have 401k at work

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errfileno Mar 12, 2019

Although law allows a payroll deduction to be allocated to the prior year's contributions until April 15, I have yet to find anywhere that is actually able to do this because the management tools don't have a way for them to make such designation.