German smartphone bank N26 now has 5 million customers, the founder of Berlin's leading fintech startup said, a big increase from the 3.5 million users it reported last summer.  

N26 was last valued by investors at $3.5 billion.

It is growing fastest in its main European markets while the US - where it launched last year - is making a positive contribution, co-founder and chief executive Valentin Stalf told Reuters. 

"We added more customers in 2019 than we did in all the prior years put together," Stalf, 34, added in an interview. 

He declined to share financials or give a market breakdown, but said growth at N26 was strongest in Germany, France and Austria, while Italy and Spain had a chance to achieve a similar rate of expansion. 

N26 has reached over 100,000 customers in Ireland, the smartphone bank said in December.

It said its  Irish customer base grew by over 152% in 2019, with the majority of signups coming from referrals of friends and family.

It also noted that during 2019, growth in the bank's female customer base outpaced that of its male customer base by over 50 percentage points in Ireland. 

The number of female customers grew by 192% last year, compared to a growth rate of 135% for its male customer base.

Meanwhile, N26 said the 25-29 age group is its largest, accounting for almost 25% of its Irish customer base, but it also said the number of N26 customers in Ireland over 65 more than doubled last year.

N26, founded five years ago, has raised a total of $670m in investment. 

Its last funding round in July 2019 gathered $170m from backers including Valar, Tencent and Insight Partners.