A further two NATO nations are estimated to be meeting or exceeding the alliance's target of spending 2% GDP on defence, compared to previous statistics.
The UK, which is one of the nine nations hitting the target, has slipped to the alliance's joint fourth-highest spender in terms of a percentage of GDP.
Despite the UK falling in the list, estimates released by NATO suggest the UK has actually increased its GDP spend from 2.13% to 2.14%.
The US remains the alliance's biggest contributor, spending 3.42% of GDP, while Bulgaria's spending has rocketed from 1.61% to an estimated 3.25%, making the country NATO's second-biggest spender in terms of a share of GDP.
Bulgaria's rise up the table comes after the country bought a new fleet of F-16 fighter jets in a deal worth around $1.3 billion.
However, reports in Bulgaria have suggested its defence spending could fall next year.
But NATO Secretary General Jens Stoltenberg argued the overall spending trend was still positive.
"If you have a huge investment, maybe your defence spending will go up, then a bit down next year - that may happen," Mr Stoltenberg said.
"But there's no doubt that the trend is up because year-by-year we are increasing and year-by-year we are adding billions to our defence spending and this is totally different from what we saw before.
"We have five consecutive years of increase across Europe and Canada."
NATO estimates that by the end of 2024, European NATO allies and Canada will have added an extra $400 billion dollars to their defence budgets since 2016.
Greece sits third in the GDP spend table with an estimated 2.28% of its GDP going on defence.
Estonia (2.14%), Romania (2.04%), Lithuania (2.03%), Latvia (2.01%) and Poland (2.00%) are the other nations believed to be hitting the spending target.
US President Donald Trump has repeatedly urged other NATO countries to spend more on defence, claiming the US protects Europe and is then "unfairly clobbered on trade".
He has previously called the arrangement a "rip-off", although he backed down over threats to pull the US out of NATO after other leaders agreed to increase defence spending "like they never have before" in July last year.
Meanwhile, estimates for France and Germany see defence spending at 1.84% and 1.38% GDP respectively.
Spain is estimated to have spent 0.92%, just less than Belgium (0.93%).
Luxembourg was at the bottom of the list with a GDP spend of 0.55%.
NATO is made up of 29 countries, although the newly named Republic of North Macedonia is expected to join the alliance by next spring.
Formed in the aftermath of the Second World War, NATO's original goals were to secure peace in Europe, promote cooperation among its members and to counter the threat posed by the USSR, also known as the Soviet Union.
Cover image: NATO's Exercise Trident Juncture (Picture: NATO).