What is my net worth?

I feel like I've been working on My IRA contribution goal for a long time. Because I am getting anxious to get this goal accomplished, I just changed my contribution for August to $1,800 instead of $1,200 so I can get this goal done faster.  My plan is to invest another $1,800 on September 1st, which bring my contributions to $5,000 for the year. 

Since I post at the beginning of each month to report on the pay the taxes challenge and my IRA asset allocation and balance,  I was thinking I should have something to report on mid-month. I've seen other websites report on their net worth, so I thought I'd give it a try.

I had created a spreadsheet with my estimated net worth back on March 1st (I didn't post it here), and this is what that looked like:

Assets:
Approximate value of house: $196,000
Roth IRA: $18,853
Simple IRA: $4,000 (estimation)
Savings: $11,500 (estimation)

Liabilities:
Mortgage(s): $204,278

Total net worth: $26,075

Here are the numbers today:

Assets:
Approximate value of house: $183,600
Roth IRA: $20,110
Simple IRA: $4,759 (June 30 statement)
Savings: $6,038 (not including money set aside for property taxes)

Liabilities:
Mortgage: $183,734

Total net worth: $30,773

Difference from March 1: $4,698

I thought I'd see a significant improvement, but it's the value of our house that really messed it up.  If the house value would have just stayed the same, it would have been an improvement of  $17,098.  So I should be able to be proud of myself for that.

I didn't include my husband's retirement savings (I only get updates on that every quarter anyway). So to make this easier to calculate, I'll leave it out for now.  I'll post my numbers because it'll keep me motivated to continuously improve the number!  Maybe I'll leave off the house value in the future because it's right around break even and just concentrate on the value of my savings and investments. I don't know.  What is the proper way to calculate net worth?