Taking apart the CBO estimates of the net costs of Obamacare - estimate of $1.3tn over 10 years is far too low

The CBO estimates that the net cost of Obamacare will be $1,363bn from 2014 to 2023.
This is a wildly optimistic forecast for the following reasons:-

CBO are estimating that only 22% of the currently uninsured will take up the offer of heavily subsidized insurance in 2014.
For the lowest earners, the subsidies mean that premiums will be less than $600 a year or $50 a month.
Other estimates are that 60% of the uninsured will enrol in Obamacare. This is far more realistic - Obamacare will subsidize 75%+ of non elderly wage earners that do not have health coverage from their employer.

CBO estimates that a maximum of 45% of the otherwise uninsured will enroll in Obamacare by 2017 (the fines reach a maximum in 2016).
The drastic penalties for not enrolling in Obamacare will ensure that it will be higher - the fines are 2.5% of salary, plus fines for uninsured children of half the adult rate.

The CBO is estimating that the average subsidy per person will be just over $5,000 a year in 2014, rising to $7,900 in 2023.
This looks a little low and probably does not take account of the fact that the currently uninsured will have a higher preponderance of existing conditions than the general population.

The other factor in the cost of subsidies, is that Obamacare will also subsidize deductibles for those earning 250% of the poverty level and below (around $29,000 for an individual and $58,000 for a family).
Insurers are generally limiting premium price rises (they are still going up by an average of 30% to 100%) and putting the increases more on the deductibles, so the deductible subsidies could become very significant.
http://www.kaiserhealthnews.org/features/insuring-your-health/2013/070913-michelle-andrews-on-cost-sharing-subsidies.aspx
http://hotair.com/archives/2013/10/14/if-you-think-the-obamacare-exchanges-and-premiums-were-bad/

The CBO does not seem to be taking account of the demographic shift over the next 10 years.
A large number of 40 and 50 year old baby boomers will get 10 years older and need more healthcare.

There are a number of other factors that the CBO is not taking account of, as detailed in here :-
http://ian56.blogspot.com/2013/10/obamacare-will-increase-budget-deficit.html
http://ian56.blogspot.com/2013/10/obamacare-myths-facts-and-unknowns.html

The increase in the deficit due to Obamacare is likely to be around $300bn in 2014.
As per the CBO, future years will have a larger detrimental effect on the deficit.
A more likely estimate of the net costs of Obamacare from 2014 to 2023 is $3.5tn+.

The above are only the direct costs associated with Obamacare.

There will be a number of indirect costs (estimate unknown) due to the following :-
Lower GDP growth
Higher unemployment
Lower tax revenues
More people on Food Stamps as a result of being put on part time working so employers avoid Obamacare fines
Higher welfare payments (via more unemployment benefits, food stamps etc.) 

The CBO estimates
http://www.cbo.gov/sites/default/files/cbofiles/attachments/44190_EffectsAffordableCareActHealthInsuranceCoverage_2.pdf

N.B. it is not unusual for the CBO to issue wildly optimistic forecasts and inaccurate projections.

E.G.
The CBO assumes there will NEVER be another recession.
The CBO is estimating average growth rates for 2014 to 2023 at over 4% when even during the boom years between 1950 and 1970 growth only averaged 3.3%.
Growth since 2001 has averaged just under 2%.
The CBO assumes the economy will work towards full employment (less than 5% unemployment), even if government policy is actually increasing future unemployment (as it is now).
U6 unemployment is now at 14%.
Real unemployment, including those who have given up looking for work because decent paying jobs just aren't out there, is now at 23%.