The number of NATO nations meeting or exceeding the alliance's target of spending 2% of their gross domestic product (GDP) on defence has decreased, according to the latest official estimates.
The UK, one of 10 nations believed to be hitting the target, is fourth in the list of proportional spending.
A real change annual estimate of 4.1% spending within the military alliance has seen members contributing 0.6% more than last year.
NATO data estimates UK defence spending as a percentage of GDP (gross domestic product) to have fallen from 2.32% in 2020 to 2.29%, the estimated figure for 2021.
The 2020 estimates, released in March, suggested there had been a UK defence spending boost in 2019 from 2.1% to 2.32%.
Notably, the data shows the United States has fallen behind Greece in proportional spending, contributing 3.52% of GDP compared to Greece's 3.82%.
Croatia is in third place with 2.79%, while Estonia (2.28%), Latvia (2.27%), Poland (2.1%), Lithuania (2.03%), Romania (2.02%) and France (2.01%) also make up the 10 nations meeting NATO's proportional 2% target.
Canada sits at 25th on the list, spending 1.39% of its GDP on defence.
NATO's Secretary General Jens Stoltenberg has called on defence spending to increase within the alliance.
This week, a summit in Brussels will see leaders discuss issues such as Russia, China and climate change.
The increase in 2021 is estimated at 4.1% in real terms, compared to 3.7% in 2019 and 3.5% in 2020.
Watch: NATO Secretary General Jens Stoltenberg previews the latest NATO summit.
Germany is hitting 1.53% of GDP when it comes to defence spend – below the NATO guideline.
Luxembourg was at the bottom of the list with a GDP spend of 0.57%, now the only nation estimated to be below 1%, while Belgium (1.12%) and Spain (1.02%) also lie in the bottom three.
NATO is made up of 30 countries, an increase of one after the Republic of North Macedonia (1.61%) joined in 2020.
Iceland, which does not have any armed forces, was not featured on the list.
Formed in the aftermath of the Second World War, NATO's original goals were to secure peace in Europe, promote co-operation among its members and counter the threat posed by the USSR, also known as the Soviet Union.
Cover image: Tanks taking part in training in Estonia as part of NATO's enhanced Forward Presence Battlegroup last month (Picture: NATO).