Pay Estimate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Retirement Pay
Estimated Rank[1] O-3 O-3 O-3 O-3 O-4 O-4 O-4 O-4 O-4 O-5 O-5 O-5 O-5 O-5 O-5 O-5 O-5 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 O-6 Monthly
Base Pay 3407.4 3407.4 3862.8 4169.4 4852.5 4852.5 5130.3 5130.3 5428.2 5825.7 6113.1 6113.1 6324 6324 6596.4 6596.4 7013.7 7683.6 8075.1 8075.1 8466.3 8466.3 8688.9 8688.9 8914.5 8914.5 9351.9 9351.9 9351.9 9351.9 7013.925
Housing allowance[2] 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200 1200
Optometry Pay 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
Subsistence 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76 202.76
FAAO Pay 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300 300
CE reimbursement 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000 1000
Retention Pay 6000 6000 6000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 38000[3] 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000 8000
Loan Repayment Program 0 0 24000[4] 24000[5] 24000[6] 24000[7] 24000[8] 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Yearly times 25 years
Total Yearly Gross 65921.92 65921.92 95386.72 104665.9 112863.1 112863.1 116196.7 92196.72 95771.52 100541.5 103990.3 103990.3 106521.1 106521.1 139789.9 109789.9 114797.5 122836.3 127534.3 127534.3 132228.7 132228.7 134899.9 134899.9 137607.1 137607.1 142855.9 142855.9 142855.9 142855.9 84167.1 2,104,178
Total Career Gross 3506529.6
What you have to make in Civian life to equal USPHS benefits.
2 extra weeks paid vacation[9] 2535.46 2535.46 3668.72 4025.61 4340.89 4340.89 4469.10 3546.03 3683.52 3866.98 3999.63 3999.63 4096.97 4096.97 5376.54 4222.69 4415.29 4724.47 4905.17 4905.17 5085.72 5085.72 5188.46 5188.46 5292.58 5292.58 5494.46 5494.46 5494.46 5494.46
Not having to pay malpractice ins.[10] 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700 700
IHS housing $200 rent[11] 4800 4800 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
30 year retirement[12] 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808 23808
Total Compensated Gross 97765.378 97765.38 123563.4 133199.5 141712 141712 145173.8 120250.7 123963 128916.5 132497.9 132497.9 135126.1 135126.1 169674.5 138520.6 143720.8 152068.8 156947.5 156947.5 161822.4 161822.4 164596.4 164596.4 167407.7 167407.7 172858.4 172858.4 172858.4 172858.4
Total Compensated Career Gross 4386236.1
Please note, the above numbers represent year 2008 dollars.  There has been no adjustment made for inflation.
Also note, these numbers are NOT official numbers from the USPHS.
Theoretical promotion schedule from O-3 to O-6; promotion is not guaranteed nor placed on a specific timeline.
For USPHS base pay see:  http://dcp.psc.gov/PDF_docs/2004PayChart.pdf
The best place to estimate your pay is http://www.dod.mil/militarypay/
Specifically, try the page: http://www.dod.mil/militarypay/pay/calc/index.html 
Remember, the above numbers are just to give you an idea of what you can make.
Remember that promotion is not guaranteed, nor is there necessarily any time line for promotion
Assumptions: that you make a 30 year career in USPHS, that you get LRP, Housing allowance is variable among areas
[1]

Assumes an arbitrary but regular promotion; please do not take this as what you can expect.  Several factors play into getting promoted.  Promotion is not automatic.
[2]

This number can change depending on where you live
[3]

8000 retention bonus plus 30,000 career status bonus for committing to at least 20 years in USPHS
[4]

20000 towards loans and 4000 to IRS for tax liability
Assume only $100K in loans
[5]

20000 towards loans and 4000 to IRS for tax liability
Assume only $100K in loans
[6]

20000 towards loans and 4000 to IRS for tax liability
Assume only $100K in loans
[7]

20000 towards loans and 4000 to IRS for tax liability
Assume only $100K in loans
[8]

20000 towards loans and 4000 to IRS for tax liability
Assume only $100K in loans
[9]
Assume most ODs get 2 weeks paid vacation, and since a CCO gets 30 days paid vacation per year, you could extrapolate those extra 2 weeks as income
[10]
Based on my current malpractice premiums
[11]
Assume $600 average rent, so living in IHS Housing (assuming $200 rent) saves you $400/month
Please note, not all IHS housing is $200 per month, it may be more depending on location.
I assume you only rent for 2 years and then you buy a house after that.
[12]
Assume that you would have to invest $23,808 per year with a  "balanced portfolio" of investements (http://cgi.money.cnn.com/tools/retirementplanner/retirementplanner.jsp)
and $14,000 per year of Soc. Sec. benefits to achieve $84,167 per year during retirement.