McCullum currently has 794 ratings points and leads second-ranked Chris Gayle of West Indies by just two ratings points.
Gayle will be part of the West Indies squad that plays Australia in a one-off T20I match at Brisbane on Wednesday, 13 February. But despite the narrow gap between the two, McCullum will have the edge to retain the number-one rank as he will have two more matches than Gayle.
The other batsmen in the top 20 likely to be in action during the two series are Shane Watson in fourth place, David Warner in fifth, Eoin Morgan in ninth and Alex Hales in 14th.
The bowlers' table is headed by Pakistan's Saeed Ajmal, followed by Sri Lanka's Ajantha Mendis and Graeme Swann of England.
Swann will be missing in action during the series against New Zealand.
New Zealand’s Nathan McCullum (fifth), Shane Watson of Australia (eighth), West Indies’ Sunil Narine (ninth) and England captain Stuart Broad (20th) are the other bowlers likely to feature in the forthcoming T20Is and will be hoping to improve upon their rankings.
Shane Watson will start as the number-one ranked all-rounder, with Pakistan's Mohammad Hafeez in second place and Yuvraj Singh of India in third.
Reliance ICC Test Championship Table
Sri Lanka is the clear leader on the Reliance ICC T20I Championship Table with 131 ratings points, nine ratings points ahead of second-placed ICC World Twenty20 2012 champion West Indies.
Sri Lanka will continue to head the table irrespective of how the forthcoming matches will pan out, but a lot of reshuffle is expected in the middle of the table.
At best, West Indies can hope to reduce the gap with Sri Lanka to seven ratings points if it beats Australia in the one-off match. But if West Indies was to lose the match, it would drop as many five ratings points to end at 117 ratings points, same as South Africa. But West Indies will be ranked higher than fourth-ranked South Africa by fraction of a point.
If England wins all three matches against New Zealand it will gain five ratings points to end at 123 ratings points, which could potentially give it second place if West Indies loses to Australia in the one-off match.
On the other hand, if New Zealand was to win all three matches against England, then it could gain as many 10 ratings points to end at 108 ratings points.
The final position for all four teams - Australia, England, New Zealand and West Indies - will be determined by the results in the two series.
To find out exactly how the forthcoming series will affect the T20I Championship Table, please click here. The T20I and ODI Championship tables are updated after every match, unlike the Test Championship table, which is updated after every series.
Upcoming Fixtures
New Zealand v England
9 Feb-1st T20I, Auckland (D/N)
12 Feb-2nd T20I, Hamilton (D/N)
15 Feb-3rd T20I, Wellington (D/N)
Australia v West Indies
13 Feb-One-off T20I, Brisbane (D/N)
