About this tool
Runway is the most-watched startup metric. Less than 12 months: time to start fundraising. Less than 6 months: emergency mode. Healthy: 18-24 months. Growing revenue extends runway by reducing net burn each month - model it explicitly when fundraising.
How it works
Enter cash, monthly gross burn (all expenses), monthly revenue, and revenue growth rate. The calculator simulates each month and shows when you reach breakeven or hit zero cash.
Business profitability basics
| Metric | Formula | Healthy range |
|---|---|---|
| Gross margin | (Revenue - COGS) / Revenue | Ecommerce 40-60%; SaaS 70-85% |
| Contribution margin | (Revenue - variable costs) / Revenue | 30-50% for sustainable scaling |
| Operating margin | Operating profit / Revenue | 10-20% mature business |
| Net margin | Net income / Revenue | 5-15% typical small business |
| CAC (Customer Acquisition Cost) | Total marketing / new customers | Below 1/3 of LTV |
| LTV (Lifetime Value) | Avg order x purchases per year x lifetime | 3x CAC minimum |
| Payback period | CAC / monthly contribution | Under 12 months |
| Churn rate | Customers lost / customers at start | Under 5%/month consumer, under 1%/month B2B |
Pricing levers
- Cost-plus: add margin to COGS. Simple but ignores willingness to pay.
- Competitor-anchored: position vs market average. Good for commodity products.
- Value-based: price as % of value delivered (e.g., 10% of customer's savings). Highest margin but requires defensible value calculation.
- Tiered: good/better/best. The middle tier typically captures 60-70% of buyers (decoy effect).
- Freemium: free entry, paid premium. Works for SaaS where marginal cost is near zero. Conversion 2-5% is typical.
Where the money actually goes
Typical breakdown for a $100 ecommerce sale:
| Component | $ per $100 sale | Notes |
|---|---|---|
| COGS (product + packaging) | $35-50 | Depends on margin tier |
| Shipping (in + out) | $8-15 | If free shipping to customer |
| Payment processing | $2.5-3.5 | Stripe / PayPal ~2.9% + $0.30 |
| Platform fees (Amazon, Shopify, etc.) | $0-15 | Amazon FBA ~15% referral + FBA |
| Ad spend (variable per sale) | $15-30 | Above-average for ecom |
| Returns + refunds | $2-8 | Apparel up to 20% |
| Operating costs / overhead | $5-10 | Office, software, salaries |
| Net profit | $5-15 | Slim - that's why volume matters |
The fast path to profitability
- Raise prices first - the highest-margin lever. Most products are underpriced by 10-20% relative to willingness to pay.
- Optimize the bestsellers - 80% of profit comes from 20% of SKUs. Cut tail products.
- Reduce returns - better photos, better size charts, better descriptions. Returns are pure cost.
- Renegotiate suppliers at volume thresholds - many manufacturers offer 5-15% discounts at 500/1000/5000 units.
- Reduce ad waste - exclude non-converting keywords/audiences. Most accounts waste 20-40% of spend.
The formula explained
This calculator uses the following formula:
net_burn = gross_burn - revenue; runway = cash / net_burn (or longer with growing revenue)
The reason this formula works is rooted in the underlying physics, finance, or biology of the problem. Behind every calculator is a published, peer-reviewed equation or a widely accepted convention. We do not invent formulas; we apply standard ones from textbooks, government tables, professional bodies, and academic literature.
If you are curious about the math, the simplest way to verify is to plug in two known numbers and compare against a known result. The calculator should match published examples to within rounding precision.
Frequently asked questions
Gross vs net burn?
Gross: all expenses regardless of revenue. Net: gross minus revenue (the actual cash drop per month).
How much runway should I raise?
18-24 months. Less = fundraising distracts. More = dilution and possible mismanagement.
Is growing revenue 'real' runway?
It reduces burn each month. Always model both 'flat' and 'growing' scenarios - investors look at flat to be safe.
Layoffs to extend runway?
Last resort. Typical: cut to extend to 18 months runway, paired with refocused product/sales effort. Communicate openly.
What gross margin do I need to survive?
Bare minimum 30% to cover variable costs. 40%+ to fund growth. Below 30% you're essentially a high-revenue zero-profit business. Software typically has 70-85% gross margin which is why it scales so well.
How do I price a product I'm launching?
Start at 50-100% above your cost (depending on perceived value), test with 50-100 customers, then iterate. Most early-stage businesses under-price. If 80%+ accept the price without negotiating, you're too cheap.
What's a realistic ad spend ratio?
Direct-to-consumer ecommerce: 15-25% of revenue is typical for growth. Lower (5-10%) for established brands with strong organic. Higher (30%+) for very new brands fighting for awareness. Watch contribution margin after ads, not just ROAS.
Is dropshipping still profitable?
Margins have compressed since 2020 due to ad costs and saturated niches. The dropshipper-must-ship-fast era is largely over for Western markets. Profitable models in 2026 typically own inventory, have a brand, or operate in niches with high margins (handmade, made-to-order, specialty).
How do I calculate LTV?
Average order value x purchase frequency per year x average customer lifespan in years. For repeat-business categories (consumables): typically 3-7 years. For one-time-purchase products: LTV = single order value. Compare LTV to CAC; aim for 3:1 minimum.
How accurate is the Runway Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Runway Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Can I use the Runway Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum.
Does the Runway Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
How do I report a bug or suggest improvement to the Runway Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours.
Can I share results from the Runway Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another runway tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.