Update (March 2016): The ONS have re-designed their website and whilst it may make it easier to navigate, the links below are no longer valid. I will update soon.

In the past I've struggled a great deal trying to navigate the ONS website, and although it's improving I thought I'd write a brief guide to understanding the National Accounts. Although GDP is measured on a quarterly basis, "new" figures are released each month. This page is for people that see a figure being reported in the news, and want to know where it's come from. In addition, I hope to raise awareness of Nominal GDP, and how to find this in the official data.

The table below shows a stable link for the three different releases. By finding the current month, you will see wherabouts the ONS are in the cycle. The Preliminary estimates tend to get more headlines because they are the first indication of the shape of the economy. So April, July, October and January tend to be when GDP figures are in the headlines. But these are subject to revision, and it's quite possible that what gets announced as a "recession" turns out not to be one.

Also, don't forget that even the "final estimate" is subject to revisions. For example, when the Final estimate of the Q2 data is released in September we tend to compare it to the Second estimate, released in August. But the September release may also adjust the data for previous quarters, such as Q1.

Calender of GDP releases	Preliminary Estimate (First Estimate)	Second Estimate	Quarterly National Accounts (Final Estimate)
Q1 (Jan, Feb, Mar)	April	May	June
Q2 (Apr, May, Jun)	July	August	September
Q3 (Jul, Aug, Sep)	October	November	December
Q4 (Oct, Nov, Dec)	January	February	March

When you click on the link you will have two options:

If you want to view the data:
- Statistical bulletin > Download PDF
If you want to download the data (or see data over a longer period):
- Reference Tables > Quarterly National Accounts Data Table

The preliminary estimate doesn't contain the same amount of information as the second and third. I believe that this will soon change, but for now:

Preliminary estimate
- See Table B1 - the second column from the right shows "Gross Domestic Product at market prices"
- The headline figure that gets reported in the news is the quarterly growth rate compared to the previous quarter - series code IHYQ
Second estimate and third estimate
- See Table A1 - this shows annual levels, quartely levels, annual change, quarterly change (compared to previous quarter), and quarterly change (compared to previous year). The headline figure has the same series code as in the preliminary estimate - IHYQ. The third column is showing Real GDP (i.e. GDP at market prices).
- We can also see estimates for NGDP (i.e. GDP at current prices) in the first column.
Note that:

NGDP = Real GDP + GDP Deflator
IHYO = IHYR + IHYU
You can also do this for annual figures (YoY change)

IHYM = IHYP + IHYS
Or quarterly figures (QoQ change)

IHYN = IHYQ + IHYT
- For full details of NGDP see Table C1. This shows "Gross Domestic Product at market prices" but measured in current prices.
  - The comparable figure to the headline GDP figure is the "percentage change , latest quarter on previous quarter" - series code IHYN
  - The figure that ties in best to NGDP targets is "percentage change , latest quarter on corresponding quarter of previous year" - series code IHYO
- Table A2 can be useful because it shows absolute levels - if you want to verify the growth rates you can calculate them yourself from this data
- Table F shows Gross Fixed Capital Formation which is essentially investment

For more, here's a guide by the Chief Economist of the ONS.

An alternative way to find annual NGDP data is to look at "Money GDP" from HM Treasury, which goes back to 1955.

Exercise

On April 25th 2013 The Guardian wrote:

George Osborne has welcomed news that Britain's economy expanded by a stronger-than-expected 0.3% in the first quarter of 2013, avoiding a triple-dip recession.

As the first estimate from the Office for National Statistics showed that a healthy performance from the services sector helped GDP growth to beat the 0.1% expected by City pundits, the chancellor said it was evidence that the coalition's policies were helping to "build an economy fit for the future".

Using the information in this post you should be able to go to download that very release, and see where the reported 0.3% figure comes from.