Cast Study - Is my math flawed?

[Mrs. Green]

My husband, who built homes in his 20s, was a software developer in his 30's/40's, is now working his "retirement" job.  He is the "building trades / woodworking" teacher at our local high school.  6 months into it, he absolutely loves the job.  He says he will not leave until he physically has to.  If I had to guess that will be when he is around 65-70 (he turns 50 in a few days).

With being a teacher, he obviously gets big chunks of time off work - 2-3 weeks for winter break, fall break, spring break, and all summer.  This is a great schedule!  I am still working (I'm 38), but I work from home which is nice (business analyst - my loser story - http://forum.mrmoneymustache.com/case-studies/cast-study-loser/)

I would like to retire early, even if my husband does not want to, because we'd like to travel and have the ability to do things together over all his breaks (like spending winter break in Florida, etc.).  So, here is what I'm thinking early retirement would look like for me, so I can have time off when my husband has time off.  I would likely get a part-time job, but with the flexibility to take off as desired. 

Here is what our monthly expenses would look like once our kids are grown (10 year old twin boys) and our mortgage / student loans are paid.   I've rounded up in most categories. 

Food   $400.00
Electricity   $150.00
Fuel   $75.00
Water $40.00
Car Insurance $25.00
Internet $30.00
Cell $30.00
Vacationing $500.00
Trash $30.00
Entertainment   $300.00
Other $250.00
Continue Retirement Savings   $1,000.00
House Insurance   $160.00

   
MONTHLY Living Expenses   $2,990.00
MONTHLY Hubby Teaching Salary   $2,000.00
Needed Each Month   $990.00

I think I could easily cover the extra $990 each month required with part-time work, but it would be nice to have enough in retirement savings to pull that amount each month.

So.... here is the math I am wondering if is flawed. I believe I can "retire" once our student loans and house are paid for.  Those are our only two debts.

House Debt   $165,000.00
Student Loan   $60,000.00

Thoughts?  Thank you so much in advance!!

[AMandM]

Assuming those income figures are after-tax amounts, one way to look at it is that your husband's salary would cover your living expenses, and your part-time work would add to the retirement savings.

The question is, would this produce enough total retirement savings to allow your husband to retire (eventually) and you also to retire from your part-time work?  How much do you have saved now?  How much do you think you will add to it before you go part-time?  On the standard 4% SWR, you would need $600k to generate enough for both of you to stop earning.

[AMandM]

I just thought of something else--where are your medical expenses?

[Viking Thor]

What are your current savings / investments? That is a big factor in the outlook.

 Also you list continue retirement savings as $1k expense, so your actual monthly costs are lower. It's great that you want to continue to invest but looks like the money you need per month is covered in husband's salary. If you have some retirement savings you could be in good shape.

[MDM]

Thoughts?

What does the simple FI calculation in the case study spreadsheet show?

Or the more elaborate calculations in cfiresim or one of the ones from Best and/or Recommended Retirement Calculator - Bogleheads.org?