The formula behind my website ROI calculator

The formula below gives you one number that matters: how much revenue your current conversion rate leaves on the table each month. Here is the exact formula, what to enter, and how to read the result honestly.

No black box. The same math is spelled out below.

The formula

Four inputs, four outputs:

currentRevenue   = traffic × (currentRate / 100) × orderValue
projectedRevenue = traffic × (targetRate / 100) × orderValue
monthlyGap       = projectedRevenue − currentRevenue
yearlyGap        = monthlyGap × 12

Where:

• traffic is monthly visitors, all sources combined
• orderValue is average revenue per conversion (order, booked job, signed retainer)
• currentRate is your measured conversion rate today, in percent
• targetRate is a realistic improved rate, capped at 15% to prevent fantasy math

That is the whole model. No attribution magic, no hidden multipliers.

A worked example (illustrative)

Suppose, purely for illustration:

• traffic = 2,000 visitors per month
• orderValue = $150
• currentRate = 1.2%
• targetRate = 2.0%

Then:

currentRevenue   = 2,000 × 0.012 × 150 = $3,600/mo
projectedRevenue = 2,000 × 0.020 × 150 = $6,000/mo
monthlyGap       = $6,000 − $3,600 = $2,400/mo
yearlyGap        = $2,400 × 12 = $28,800/yr

These are not claims about your business. They show how a 0.8-point lift compounds: same traffic, same ad spend, more captured revenue. Plug your own numbers into the formula to get your bound.

What to enter for each input

Traffic: use measured, not hoped-for. Pull last 90 days from your analytics and average it. Do not enter ad-platform clicks; use sessions that reached the site. If traffic is seasonal, run the math twice: low month and high month.

Current rate: measure the real funnel. For lead sites: qualified enquiries divided by visitors. For stores: orders divided by sessions. Exclude bot spikes and internal testing windows. If you do not track this yet, set up analytics first, then come back. Guessing the baseline makes the output decoration.

Target rate: stay conservative. Design-led rebuilds commonly aim for a 0.5–1.0 point lift on lead sites, not a 5x miracle. Keep targets above 15% off the table, and treat anything at or below your current rate as baseline: a target must exceed the baseline to mean anything.

Order value: use contribution, not revenue, when you can. If fulfillment eats 60% of a $200 order, the decision math should reflect margin. Enter gross order value for a first pass, then re-run with margin to size what a rebuild is worth to you.

How to read the result without fooling yourself

The monthly gap is an opportunity bound, not a promise. It says: if traffic and order value hold and the rate lift materializes, this is the revenue shape. Three honest checks:

1. Can the lift come from design alone? Clear hierarchy, faster loads, reduced form friction, and trust signals move rates. Pricing, offer strength, and sales follow-up also matter. Credit design with part of the gap, not all of it.
2. Does traffic quality support it? Junk traffic converts at junk rates on any design. If half your visits bounce in under 5 seconds from irrelevant keywords, fix acquisition before blaming the page.
3. What does payback look like? Divide a quoted build cost by the monthly gap. A $3,000 site against a $2,400/mo illustrative gap pays back in under two months if the lift lands. Halve the lift and re-check. If payback still works at half lift, the investment is robust.

Run your page through the site grader alongside these numbers. Low performance, SEO, or accessibility scores point to where the lift likely comes from.

When the math says "do nothing"

Sometimes the honest answer is to wait:

• Under ~500 visitors per month, rate math is noisy. Buy or earn traffic first.
• Order value under ~$20 with thin margin rarely funds custom work. Start with a Quick Fix pass instead.
• No measurement in place. Instrument analytics, collect 30 days, then decide.

Math that always says "rebuild now" would be a sales pitch. These numbers are a sizing tool. Use them that way.

From number to scope

Once you have your gap, convert it to scope:

• Gap under ~$500/mo: single-issue fixes. Speed sprint, checkout repair, or landing-section redesign in the $100–$500 range.
• Gap in the low thousands per month: full landing or business-site rebuild, $600–$5,000 depending on pages and CMS needs. Scope it against the published tiers.
• Gap with logged-in workflows behind it: that is app scope, $2,800–$12,000. Price the workflow, not the pages.

Bring these inputs to the quote. "2,000 visitors, 1.2% now, $150 order value, targeting 2%" gets you a sharper fixed price than "need more sales."

The bottom line

Traffic times rate times value, current versus target, gap times twelve. Conservative inputs, honest reading, payback at half lift. That is the entire method.

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Run your numbers with the formula above, then get a fixed quote scoped to close your specific gap.