I built a real-time penalty calculator because HMRC won't tell you what you owe

Quick background: I'm building free tools for UK freelancers at landolio.com . This one came from personal frustration. HMRC will send you a penalty notice weeks after the fact. Meanwhile, the daily £10 charges are silently racking up. There's no dashboard, no counter, no "hey, you currently owe £X" message anywhere. So I built one. What it does The calculator shows: Your exact penalty amount right now (live counter) How the penalties break down (initial £100 + daily charges) What happens at 3 months, 6 months, 12 months How much you save by filing today vs waiting The maths For anyone who missed the 31 January 2026 deadline: Day 1 (1 Feb): £100 fixed penalty Day 30+ (1 Mar): £10/day begins Day 120 (31 May): Daily penalties cap at £900 Total: £1,000 Day 183 (1 Aug): +£300 or 5% of tax due Day 365 (1 Feb 2027): +£300 or 5% of tax due As of today (17 March), that's £270 if you haven't filed. The tech Vanilla JS. No framework, no backend. Date arithmetic against known HMRC penalty dates.