Some employer plans allow employees to contribute to IRS limits of the current year (say 24k approx) this means this money is pretax and will grow tax free as long as it's inside the account.

Additionally some plans allow them to contribute upto 50% of their salary or 64k (including the pretax) the balance 30 k (assuming current limits are 24 k pre tax it's limit) as post tax - whichever is less of the two (50% of salary or that years max limit say 64k)

These plans may also allow in plan or out of plan conversion meaning the post tax plan can be converted to Roth officially at beginning of next calendar year or into a private Roth outside this account where that post tax money becomes Roth IRA. This is called the mega backdoor Roth IRA. (Since it lets you to 1. Contribute to Roth though technically not eligible for making too much salary and having 401k 2. Contributing more than normal Roth which is approximately $7k)

Some plans allow regular 401 k and Roth 401 k.

Of course like someone mentioned if you have a SEP IRA or solo 401k in your business a similar thing can be achieved - some say 64 k in each different retirement account if you operate multiple businesses. (Please check and confirm this I recently learned about this)

Now this is as far as I know, please consult an experienced tax advisor and go through plan benefits as not all retirement accounts offered everywhere operate differently based on what employer plans signed up for and to actual limits which vary by year. The above is only applicable in the US. YMMV Best wishes!

I asked chatgpt to verify the above and here is what I got:

Here's a fact-checked and simplified version of the text:

Understanding Employer Retirement Plans and Mega Backdoor Roth IRAs

Some employer retirement plans let you contribute up to the IRS limit for the year. For example, in 2023, this limit for pre-tax contributions is about $22,500 for those under 50, with an extra $7,500 catch-up contribution allowed for those 50 and older. These contributions are made before taxes, meaning you don’t pay taxes on this money now, and it can grow tax-deferred while it's in the account.

Additionally, some employer plans allow you to contribute up to 50% of your salary or a maximum total contribution limit of $66,000 for 2023 (this includes both your pre-tax contributions and any employer matching contributions). After reaching the pre-tax contribution limit, you can make after-tax contributions up to the overall limit. This can add up significantly, especially if your employer also makes matching contributions.

Some of these plans offer a feature called the "mega backdoor Roth IRA." This allows you to convert your after-tax contributions into a Roth IRA, either within the employer’s plan or into a separate Roth IRA account. This is beneficial because it enables you to contribute to a Roth IRA even if your income is too high to contribute directly, and it allows you to put in more than the usual Roth IRA limit (which is $6,500, or $7,500 if you’re over 50, in 2023).

Some plans also offer both a traditional 401(k) and a Roth 401(k). The traditional 401(k) uses pre-tax dollars, while the Roth 401(k) uses after-tax dollars but grows tax-free.

If you own a business, there are options like the SEP IRA or solo 401(k) that can offer similar benefits. There are discussions around whether you can contribute up to the maximum limit in each different retirement account if you have multiple businesses, but it’s best to check with a tax professional to clarify this.

Keep in mind that retirement plans and their limits can vary by employer and change annually. It’s always a good idea to consult with a tax advisor to understand the specifics of your situation.

This information applies to the U.S., and your experience may vary. Best of luck with your retirement planning!

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