DEV Community: NovusTools

How I built a clean Compound Interest Calculator in Vanilla JS

NovusTools — Mon, 01 Jun 2026 17:00:00 +0000

As indie hackers and developers, projecting our long-term investments and personal finance is just as important as writing code. I wanted a fast, ad-free tool for this, so I built a Compound Interest Calculator.

The Approach

I built this using 100% Vanilla JS. No server calls, no tracking scripts. Financial inputs are private and should stay strictly on the client side.

Here is a look at the core function implementing the compound interest formula:

function calculateCompoundInterest(principal, rate, years, compoundingFrequency) {
    const r = rate / 100;
    const n = compoundingFrequency;
    const t = years;

    const amount = principal * Math.pow((1 + (r / n)), (n * t));
    const interestEarned = amount - principal;

    return {
        totalAmount: amount.toFixed(2),
        totalInterest: interestEarned.toFixed(2)
    };
}

Try it out

You can use the live tool for free here: Compound Interest Calculator

Let me know what you think or if you'd add any specific financial metrics in the comments!

How I built a fast SaaS Pricing Calculator in Vanilla JS

NovusTools — Mon, 01 Jun 2026 13:00:00 +0000

As developers building micro-SaaS projects, we often need a quick way to model our pricing tiers and project potential revenue. I was tired of using complex spreadsheets, so I built a clean, client-side SaaS Pricing Calculator.

The Approach

I wanted to keep it 100% Vanilla JS for maximum performance and security. No server calls, complete data privacy for your business metrics.

Here is a quick look at how the core logic handles the MRR (Monthly Recurring Revenue) calculation:

function calculateSaaSRevenue(users, monthlyPrice, churnRate) {
    const grossMRR = users * monthlyPrice;
    const churnedRevenue = grossMRR * (churnRate / 100);
    const netMRR = grossMRR - churnedRevenue;

    return {
        grossMRR: grossMRR,
        netMRR: netMRR,
        annualRevenue: netMRR * 12
    };
}

Try it out

You can use the live tool for free here: SaaS Pricing Calculator

Let me know what you think or if you'd add any other metric calculations in the comments!

How I built a blazing fast AI ROI Calculator in Vanilla JS

NovusTools — Mon, 01 Jun 2026 11:35:39 +0000

As developers and agency owners, we often need to justify the cost of AI API integrations to clients or ourselves. I was tired of guessing the break-even points, so I built a clean, client-side AI ROI Calculator.

The Approach

I wanted to keep it 100% Vanilla JS for maximum performance and security. No server calls, complete data privacy for sensitive financial inputs.

Here is a quick look at how the core calculation logic handles the monthly cost comparison:

function calculateROI(humanHours, hourlyRate, apiCostPerMonth) {
    const currentMonthlyCost = humanHours * hourlyRate;
    const savings = currentMonthlyCost - apiCostPerMonth;

    if (savings > 0) {
        return { isProfitable: true, monthlySavings: savings };
    }
    return { isProfitable: false, monthlyLoss: Math.abs(savings) };
}

Try it out

You can use the live tool for free here: AI ROI Calculator

Let me know what you think or if you'd add any specific API pricing presets in the comments!