DEV Community: Felix ZHU

30+ free SaaS calculators for founders — revenue, CAC, churn, LTV:CAC, ROAS, conversion rate, and more. All run in your browser. No sign-up, no data collection, no tracking. Built because I was tired of blog posts that say "3:1 LTV:CAC is good"

Felix ZHU — Sun, 11 Oct 2026 05:31:38 +0000

Felix ZHU

Oct 11

30+ Free SaaS Calculators and Tools for Founders (2026)

#sass #calculator #productivity #marketing

4 min read

30+ Free SaaS Calculators and Tools for Founders (2026)

Felix ZHU — Sun, 11 Oct 2026 05:29:35 +0000

Every founder I know has the same problem: you know you should track your metrics, but pulling the numbers together takes forever.

You open a spreadsheet. You Google "what's a good LTV:CAC ratio." You find three blog posts with three different answers. You close the spreadsheet. Sound familiar?

I built Niche AI Tool because I was tired of this cycle. Instead of writing another opinion blog post, I built free calculators that actually solve the problem. All of them run 100% in your browser — no sign-up, no data collection, no tracking.

Here's the full collection.

Revenue & Metrics Calculators

The core stuff. If you only use three tools from this list, make it these three.

SaaS Revenue Calculator — MRR, ARR, runway, growth rate. The starting point for any SaaS metrics check.

MRR Growth Calculator — Month-over-month growth with CAGR. See if your growth is accelerating or decelerating.

CAC Calculator — Customer acquisition cost with payback period. Find out how long it takes to earn back what you spent to get a customer.

Churn Rate Calculator — Monthly churn with revenue impact. A 5% churn rate doesn't sound bad until you see it means 46% annual churn.

LTV:CAC Ratio Calculator — The magic ratio every SaaS founder needs. 3:1 is the floor, not the goal.

Profit Margin Calculator — Gross vs net margin breakdown. See where your money is actually going.

Conversion Rate Calculator — Website conversion rate, CPA, and revenue per visitor. Includes industry benchmarks (e-commerce 2-3%, SaaS 5-10%, B2B 2-5%).

Marketing & Ads Calculators

ROAS Calculator — Return on ad spend with break-even analysis. Find out if your ads are actually profitable.

ROI Calculator — General-purpose ROI with timeline. Good for any investment decision.

CPM Calculator — Ad cost per thousand impressions. Compare ad platforms apples-to-apples.

Email Open Rate Calculator — Benchmark against industry averages. If your open rate is below 15%, something's wrong with your subject lines or list quality.

UTM Link Builder — Campaign URL builder with presets. Stop guessing which channel is driving traffic.

AI & Developer Tools

AI Tool ROI Calculator — Are your ChatGPT, Claude, and Cursor subscriptions actually worth it? Input your hourly rate, weekly usage, and subscription stack to see your real ROI. I've had people tell me they cancelled $80/month of unused subscriptions after using this.

Stripe MCP Config Validator — Paste your MCP JSON, detect secret-key leaks before you deploy. Runs entirely in your browser, so your keys never leave your device.

Cold Email ROI Calculator — See if your cold email campaigns are actually profitable.

Cold Email Reply Rate Calculator — Benchmark your reply rates against industry data.

Reviews & Comparisons

Calculators are great for your own metrics, but what about the tools you're paying for?

I also publish data-backed reviews — every one aggregates thousands of real user ratings from G2, Capterra, and Trustpilot. No paid placements, no sponsored rankings.

Head-to-head comparisons:

Lemlist vs Instantly — Which cold email tool wins in 2026?
Jasper vs Copy.ai — AI writing tools compared
Ahrefs vs Semrush — SEO tools showdown

Deep reviews:

Jasper Review — 4.7/5 G2, but 3.5/5 Trustpilot. The rating gap tells the real story.
Instantly.ai Review
Smartlead Review

Why All Free?

Good question. Here's the honest answer:

Tool pages rank better than blog posts. People search for calculators, not opinions. Google knows this and rewards pages that satisfy the query completely.
Engagement is 10x higher. People spend 2-3 minutes using a calculator. They spend 30 seconds skimming a blog post.
No backend = no cost. All calculators are pure HTML + JavaScript, deployed on Cloudflare Pages for free. No servers, no databases, no maintenance.
Your data stays yours. Every calculator runs locally in your browser. Your revenue numbers, ad spend, and customer counts never touch a server.

Start Here

If you're new, start with the SaaS Revenue Calculator. It takes 30 seconds and will tell you more about your business than most dashboard tools.

Then check your LTV:CAC ratio. If it's below 3:1, you have a problem that no amount of growth will fix.

All tools are free, forever. No credit card, no email gate, no bullshit.

Explore all 30+ free tools →

Disclosure: This contains affiliate links. If you sign up through these links, we may earn a commission at no extra cost to you.

I Built 14 Free Calculators to Get SEO Traffic — Here's What Worked

Felix ZHU — Thu, 01 Oct 2026 09:24:08 +0000

The Problem: Blogging Takes Too Long

Like every indie hacker, I started with a blog. I wrote 30+ articles about AI tools, spent hours on keyword research, and waited for Google to notice me.

Six months later? 12 visitors a day. Most of them from my mom clicking to be supportive.

The problem was obvious: every AI tool review blog says the same thing. "ChatGPT is great for writing. Claude is great for coding. Cursor is great for..." You've read it a hundred times. I was adding noise to a noisy room.

The Pivot: Tools Instead of Articles

I had a simple realization: people search for calculators, not opinions.

When someone types "SaaS revenue calculator" into Google, they don't want a 2,000-word blog post. They want to type in their numbers and get an answer. And Google knows this — tool pages rank higher because they satisfy the query completely.

So I stopped writing reviews and started building tiny calculators. Each one took 2-4 hours. Pure HTML + JavaScript, no backend. Deployed on Cloudflare Pages for free.

What I Built (14 Tools and Counting)

Here's the current lineup:

Revenue & Metrics (the core)

SaaS Revenue Calculator — MRR, ARR, runway, growth rate
MRR Growth Calculator — month-over-month growth with CAGR
CAC Calculator — customer acquisition cost with payback period
Churn Rate Calculator — monthly churn with revenue impact
LTV:CAC Calculator — the magic ratio every SaaS founder needs

Marketing & Ads

ROAS Calculator — return on ad spend with break-even analysis
ROI Calculator — general-purpose ROI with timeline
Conversion Rate Calculator — A/B test significance checker
Email Open Rate Calculator — benchmark against industry averages
Profit Margin Calculator — gross vs net margin breakdown
CPM Calculator — ad cost per thousand impressions

AI & Developer Tools (the new direction)

AI Tool ROI Calculator — are your ChatGPT/Claude/Cursor subscriptions actually worth it?
Stripe MCP Config Validator — paste your MCP JSON, detect secret-key leaks before you deploy
UTM Builder — campaign URL builder with presets

That last one — the AI Tool ROI Calculator — is currently my favorite. Every developer I know is subscribed to 3-5 AI tools and has no idea if they're getting value. The calculator lets you check your hourly rate, weekly AI usage, and subscription stack to see your real ROI. I've had people tell me they cancelled $80/month of unused subscriptions after using it.

The Results So Far

I won't pretend this is a viral success story. It's a slow burn, but the numbers are moving in the right direction:

Traffic: From 12 visitors/day to ~150 visitors/day in 3 months
Top pages: The calculators rank on page 1-2 for their target keywords
Bounce rate: 35% (people actually use the tools, then stay to browse)
Average session: 2:40 (they calculate, then click "More Free Tools")

The key insight: tool pages have 10x the engagement of blog posts. People spend 2-3 minutes actually using a calculator. They spend 30 seconds skimming a blog post. Google sees this engagement and rewards it.

What I Learned (The Hard Parts)

1. Interlinking matters more than I thought. Every calculator page links to 5-6 related calculators. This creates a "wiki effect" where Google crawls deep into the site. I added a "More Free Tools" grid to every page, and internal traffic doubled within a week.

2. Schema is non-negotiable. Every tool page has WebApplication + FAQPage JSON-LD. The FAQ schema alone got me rich snippets within 2 weeks. For the MCP validator, I also added HowTo schema (Paste → Validate → Review), which targets "how to" search queries.

3. Local processing is a selling point. Both the AI ROI Calculator and MCP Config Validator run 100% in the browser. I put "🔒 100% Local · No Sign-up" in the hero. People actually care about this — especially for the MCP validator where they're pasting API keys.

4. Don't build tools nobody searches for. I almost built a "invoice number generator" because it was technically easy. Then I checked search volume — basically zero. Every tool I build now starts with a keyword check. If nobody's searching for it, I don't build it.

5. The "per-tool ROI" feature almost got me in trouble. In the AI ROI Calculator, I initially showed "Keep / OK / Review" labels for each subscription. Then I realized: allocating total savings proportionally to cost is mathematically convenient but logically flawed. A $20 tool doesn't necessarily save more time than a $10 tool. I changed the labels to "High / Moderate / Low" and added a big warning: "This is only a rough mathematical approximation. Real-world individual tool ROI cannot be isolated without separate A/B testing." Honesty > false precision.

The Monetization Question

Right now, these are free tools with no direct revenue. The plan is:

Traffic first. Get to 500+ visitors/day before worrying about monetization.
Affiliate links. The calculators naturally mention tools (Stripe, Shopify, AI tools) — I'll add affiliate links where relevant.
Premium templates. I already sell a Stripe MCP Prompt Pack ($19 one-time). The free validator drives traffic to it. More paid templates are coming.
Newsletter. A simple "get new free tools monthly" signup. Not launched yet, but the audience is building.

What's Next

I'm adding 1-2 calculators per month. The next ones in the pipeline:

Break-even calculator for new products
Email subject line tester (scoring, not generation)
Pricing page analyzer (paste your pricing, get conversion heuristics)

If you're an indie hacker struggling with blog traffic, I'd strongly consider the tool-pivot. It's more work upfront (you have to actually build something), but the traffic quality is dramatically higher. People don't just read your tool — they use it, bookmark it, and share it.

Built a Free SaaS Metrics Calculator — Here's the Math Behind It

Felix ZHU — Thu, 10 Sep 2026 11:54:59 +0000

As a developer, I hate spreadsheets.

Every time I needed to calculate runway, LTV, or CAC payback for a project, I'd open Google Sheets, build a formula, and inevitably mess up the cell references. After the third time I accidentally calculated runway using the wrong burn rate, I decided to build a tool.

The result: a free SaaS Revenue Calculator that runs entirely in the browser.

The Math Behind the Metrics
Here's what the calculator computes and how.

Runway
javascript
// Runway = Cash in bank / Net monthly burn
const runway = cashInBank / netBurn;

// Net burn = Monthly costs - MRR
const netBurn = monthlyCosts - mrr;

// If netBurn is negative, you're profitable and runway is infinite
if (netBurn <= 0) return Infinity;
Runway tells you how many months until you run out of cash. If your MRR exceeds operating costs, you're profitable and runway is effectively infinite.

LTV (Lifetime Value)
javascript
// LTV = ARPU / Monthly churn rate
const arpu = mrr / activeCustomers;
const ltv = arpu / monthlyChurnRate;
LTV is how much revenue an average customer generates before they churn. Higher is better. A healthy LTV:CAC ratio is 3:1 or higher.

CAC Payback
javascript
// CAC Payback = CAC / (ARPU * Gross Margin)
const cacPayback = cac / (arpu * grossMargin);
CAC payback is how many months it takes to recover acquisition costs. Under 12 months is good. Under 6 months is excellent.

Why I Built This
I was tired of:

Manual calculations — Building the same formulas in every new spreadsheet

Opaque tools — Existing calculators that don't show their math

Paywalls — Tools that charge $50/month for basic arithmetic

The calculator is free, runs locally, and shows you exactly how each metric is computed.

Technical Implementation
The calculator is a single HTML file with vanilla JavaScript. No frameworks, no build step, no dependencies. It runs entirely client-side — your financial data never leaves your browser.

Key design decisions:

Real-time updates: Every input change recalculates all metrics instantly

12-month projection: Uses compound growth to project MRR forward

Health indicators: Each metric shows a green/yellow/red status based on benchmarks

When to Use This
Before a fundraise — Investors will ask about LTV:CAC, CAC payback, and net burn. Get your numbers straight.

When deciding to hire — See how adding a salary affects your runway.

When evaluating churn — Model how reducing churn from 5% to 3% changes LTV and runway.

→ Try the calculator

FAQ
Can I self-host this?

The calculator is a static HTML file. You can save it locally and run it offline.

Does it store my data?

No. Everything runs in your browser. No server calls, no analytics, no storage.

What's Next
I'm planning to add:

Scenario comparison (side-by-side what-if analysis)

Export to CSV/PDF

Cohort retention modeling

If you have feature requests, let me know.

Disclosure: This article contains affiliate links. If you sign up through these links, we may earn a commission at no extra cost to you.