The maximum contribution limit for a solo 401(k) plan for 2022 is $58,000 or 100% of the participant's earned income, whichever is less. For someone who is over 50 years old, an additional catch-up contribution of $6,500 can be made for a total maximum contribution of $64,500.
In your case, with a Schedule C income of $11,400 and W-2 wages of $3,100, your earned income is $14,500. Therefore, the maximum contribution you can make to your solo 401(k) plan for 2022 would be $14,500.
As for your Roth IRA, the contribution limit for 2022 is $6,000 with an additional catch-up contribution of $1,000 for those over age 50, for a total of $7,000.
It is true that the sum of the maximum IRA and 401(k) contributions will be the same regardless of how much you put in the IRA, but the contribution limits are different for each account type.
For 2023, the contribution limit for a solo 401(k) plan is $61,000 or 100% of the participant's earned income, whichever is less. For someone who is over 50 years old, an additional catch-up contribution of $6,500 can be made for a total maximum contribution of $67,500.
Given your projected figures for 2023, with gross earnings from employment of $25,000, employment 401(k) deferral of $12,500, and Schedule C net earnings of $14,000, your earned income would be $26,500. Therefore, the maximum contribution you can make to your solo 401(k) plan for 2023 would be $26,500. As you already have contributed $12,500 to the 401(k) plan of your employer, you can contribute $14,000 to your solo 401(k) plan.
It is important to note that these are the maximum contribution limits and you may choose to contribute less if you so desire. Additionally, you should also consider the income limits for Roth IRA contributions, as these limits may affect your ability to contribute to a Roth IRA.
It's always a good idea to consult a financial advisor or tax professional to ensure that you are making the best decisions for your financial situation and to ensure compliance with all tax laws and regulations.