Last year I unintentionally overstayed by two days because I didn't see validity is different from duration. At Frankfurt airport I got to know when I was about to exit and had to pay 110eur. Will it affect my future Schengen visa. There is no other stamp just nirmal exit stamp. This thing I need to tell when applying for uk visa?
You need to answer truthfully. The UK visitor visa application asks about travel history over the past 10 years (date and length of visit). It doesn’t specifically ask about overstays, but it will be obvious from your entry/exit stamps.
There is also a section that asks whether you’ve ever had ‘a caution, warning, reprimand or other penalty’. IMHO I would declare the fine here.