using the CSS to see the effect of both salaries combined

[johnhenry]

I hope I'm able to make this question make sense.  I'm trying to use the CSS spreadsheet to run several possible scenarios to "get a feel" for what income thresholds our family may want to target in retirement.
The base scenario I'm using (on the 2020 version of the CSS) is MFJ, 2 adults age 40, 3 children (for all boxes that ask about kids).

When I enter $26K for Salary 1 in cell B3, I can see in G32 that the net tax is (-$10,021) and the table and graph show me what I want to see (using B3 (salary 1) for the X-axis).  For the most part, the marginal rate rate is -52.35% up to about $14,520 income, then -7.35% up to $24860.  For that scenario, those are the numbers that are important to me.  It tells me that we get compensated with tax credits really well for any income up to $14,520, then to a lesser degree up to $24,860.  On income over that, the marginal rate becomes positive, making it less attractive to seek income over that threshold.

But if I tweak the spreadsheet to split the $26K in income between self and spouse, the graph using B3 and the chart with marginal and cumulative rate no longer make sense (to me, for the purpose of understanding the marginal value of each dollar the family is earning). I understand that the graph and chart are different because its is just B3(salary 1) on the X-axis...  But is there a way to see the numbers for both earners combined??  For the purpose of this exercise, that's what's important, right?   In this scenario, the net tax in cell G32 still shows (-$10,021), indicating the tax is indeed the same.

For this simple scenario, I'm sure I could get what I'm after by just leaving all the income in the column of earner 1, but some of the scenarios I'm trying to compare to this base scenario involve one or both spouses contributing to employer 401(k), or have both spouses with some Schedule C income, but also funding Simple/Solo 401(k).

Can someone point me in the right direction???  I'm tempted to just load the totals for the whole family into the column for earner 1, since it seems most of the contribution limits aren't checked against IRS rules..... but I'm not sure doing that would necessarily give accurate results for all scenarios.

[MDM]

I hope I'm able to make this question make sense.  I'm trying to use the CSS spreadsheet to run several possible scenarios to "get a feel" for what income thresholds our family may want to target in retirement.
The base scenario I'm using (on the 2020 version of the CSS) is MFJ, 2 adults age 40, 3 children (for all boxes that ask about kids).

That's a reasonable thing to study.  Do however keep in mind the old saying, "don't let the tax tail wag the dog."  E.g., the "spendable income" (cell D73) always increases as Salary #1 increases.

When I enter $26K for Salary 1 in cell B3, I can see in G32 that the net tax is (-$10,021) and the table and graph show me what I want to see (using B3 (salary 1) for the X-axis).  For the most part, the marginal rate rate is -52.35% up to about $14,520 income, then -7.35% up to $24860.  For that scenario, those are the numbers that are important to me.  It tells me that we get compensated with tax credits really well for any income up to $14,520, then to a lesser degree up to $24,860.  On income over that, the marginal rate becomes positive, making it less attractive to seek income over that threshold.

If you are planning ahead, using the 2021 version might be worthwhile.  There have been significant changes in tax law between the years.

But if I tweak the spreadsheet to split the $26K in income between self and spouse, the graph using B3 and the chart with marginal and cumulative rate no longer make sense (to me, for the purpose of understanding the marginal value of each dollar the family is earning). I understand that the graph and chart are different because its is just B3(salary 1) on the X-axis...  But is there a way to see the numbers for both earners combined??  For the purpose of this exercise, that's what's important, right?   In this scenario, the net tax in cell G32 still shows (-$10,021), indicating the tax is indeed the same.

Possibly, depending on exactly what it is you want to see - the tail-wagging comment above still applies.  If, for example, you wanted to see what happens as both salaries are identical and increase together, using =B3 in cell C3 would do that.  Because each dollar of salary #1 also increase salary #2 by $1, that doubles the marginal rate when salary #1 is the x-variable.

For this simple scenario, I'm sure I could get what I'm after by just leaving all the income in the column of earner 1, but some of the scenarios I'm trying to compare to this base scenario involve one or both spouses contributing to employer 401(k), or have both spouses with some Schedule C income, but also funding Simple/Solo 401(k).

Can someone point me in the right direction???  I'm tempted to just load the totals for the whole family into the column for earner 1, since it seems most of the contribution limits aren't checked against IRS rules..... but I'm not sure doing that would necessarily give accurate results for all scenarios.

Does any of the above help?