5 Free Financial Calculators I Built That I Actually Use Every Month

Jun 26, 2026 · 6:16 AM UTC ·2 min read · 0 reactions · 0 comments · 32 views

#fintech #webdev #tools #javascript #FinCalc AI #US #financalcai.com

TL;DR · WeSearch summary

The author built five free financial calculators that they use every month, including a mortgage calculator, compound interest calculator, retirement calculator, ROI calculator, and debt payoff calculator. These calculators are designed to handle edge cases and provide useful insights, such as the benefits of bi-weekly mortgage payments and the costs of delaying investments. The calculators are available for free at financalcai.com, with no signup or email required, and work on mobile devices.

Key facts

▪The mortgage calculator shows the full amortization schedule and highlights the benefits of bi-weekly payments, which can save ~$65K in interest on a $400K mortgage at 6.5%.
▪The compound interest calculator demonstrates the importance of starting investments early, with a 5-year delay costing $170K in potential earnings.
▪The retirement calculator uses a Monte Carlo simulation mode to estimate the sustainability of retirement funds, revealing a ~5% failure rate for the 4% rule over 30-year retirements.

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Original publisher	DEV.to (Top)
Canonical URL	https://dev.to/dayu2333jinyul/5-free-financial-calculators-i-built-that-i-actually-use-every-month-15bb
Publication time	Fri, 26 Jun 2026 06:16:35 +0000
Retrieval time	2026-06-26T06:37:29.198Z
Last seen	2026-06-26T06:37:29.198Z
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Opening excerpt (first ~120 words) tap to expand

try { if(localStorage) { let currentUser = localStorage.getItem('current_user'); if (currentUser) { currentUser = JSON.parse(currentUser); if (currentUser.id === 3960002) { document.getElementById('article-show-container').classList.add('current-user-is-article-author'); } } } } catch (e) { console.error(e); } dayu2333-jinyul Posted on Jun 26 5 Free Financial Calculators I Built That I Actually Use Every Month #fintech #webdev #tools #javascript 5 Free Financial Calculators I Built That I Actually Use Every Month I built FinCalc AI after realizing I was maintaining the same Excel spreadsheets for years — mortgage amortization, compound interest projections, retirement math.

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