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Join the waitlist
Free tool

Waitlist growth calculator, with referrals.

Put in your signups per day, how many people confirm, how many share their link and what that brings in. See how big the list gets by launch day, week by week, and how much of it comes from referrals.

It runs in your browser. Nothing you type is sent or stored.

Your numbers

These are example numbers. Replace them with your own.

From your own posts, newsletter and search. Use an average for the whole period.

Use 0 for a new list. People already on it can share their link from day one.

Launch day is the last day counted. Referrals that would arrive later don’t count.

With double opt-in, people count once they click the link in the confirmation email.

Anyone who shares it at least once, anywhere.

An average over the whole period. Only the friends who then confirm count as referrals.

Sharing fades. Half of a sharer’s friends sign up within this many days, half of the rest in the next period, and so on.

On your list at launch

1,813signups, 1,269 of them confirmed
Without referrals
1,200
Through referral links
613 (34% of the list)
Referrals that count (the friend confirmed)
429
Referral signups still to come after launch day
148
Viral coefficient

K = 0.42

70% confirm × 20% share × 3 friends

Each confirmed person brings in 0.42 confirmed people on average. By launch day, every 100 of your own signups have become 151. With unlimited time it would be 172.

List size at the end of each week
  • Without referrals
  • Through referral links

Weeks along the bottom. The last bar is launch day, day 60.

Show the numbers per week
WeekDayWithout referralsThrough linksTotalConfirmed
1714015155109
21428058338237
321420121541378
428560196756529
535700279979685
6428403681,208846
7499804621,4421,009
8561,1205581,6781,174
9601,2006131,8131,269

Waitlark counts referrals the same way: a referral counts once the friend confirms by email. How referrals work in Waitlark

How the calculator works

The calculator follows each day’s signups as a group, or cohort, from the day they join until launch day. It uses the same rule as referrals in Waitlark: a referral counts once the friend confirms by email.

The formula
K = confirmation rate × share rate × friends per sharer
With the example numbers: 0.7 × 0.2 × 3 = 0.42.
Long-run multiplier = 1 ÷ (1 − K), when K is below 1
1 ÷ (1 − 0.42) ≈ 1.72, so every 100 of your own signups grow to about 172.

Step by step

  1. Each day, your own signups join the list, plus the friends who arrive through referral links that day.
  2. That day’s signups confirm at the confirmation rate. Of the people who confirm, the share rate shares their link.
  3. Each sharer brings in the number of friends you set, spread over the days after: half within the half-life, a quarter in the period after that, and so on.
  4. Those friends go through the same steps, so referrals bring in more referrals. Every day’s cohort adds friends to the days after it.
  5. On launch day the count stops. Friends who would arrive later are shown on their own line and don’t count.

Why 1 ÷ (1 − K)

Say you bring in 100 people yourself. Through referrals they bring in 100 × K more, those bring in 100 × K × K, and so on. Added up, that’s 100 ÷ (1 − K). At K = 0.42, your 100 grow to about 172. Before launch there’s less time for all those rounds, so the number on launch day is lower. A short half-life gets more rounds in before launch; a long one leaves more for after.

Assumptions

  • The rates are the same for everyone, every week. In practice a post or a newsletter brings a burst of signups and of sharing.
  • Your own signups come in evenly, so use an average per day.
  • People confirm on the day they sign up and start sharing the day after.
  • Friends who sign up through a link confirm at the same rate as everyone else.
  • There’s always someone new to tell. Real circles overlap, so friends of friends are often on the list already.
  • Nobody leaves, and no signups are removed as fake.

Treat the result as a rough guide. Run it again with your own numbers after the first week or two, and before you plan the first batch of invites. For the rules and rewards that make people share, read the guide to a referral waitlist.

Common questions

What is the viral coefficient (K) of a waitlist?
The average number of new confirmed people that each confirmed person brings in. Here it’s the confirmation rate × the share rate × friends per sharer: 70% × 20% × 3 = 0.42 means every 100 confirmed people bring in 42 more.
What is a good K-factor for a waitlist?
There’s no fixed benchmark. Read K as a multiplier on the signups you bring in yourself: over a long run, K = 0.2 adds about a quarter on top and K = 0.5 doubles them. K above 1 is rare, and it doesn’t last when it happens.
Why does a referral only count once the friend confirms?
Unconfirmed signups include typos, fake addresses and people who changed their mind, and counting them would reward cheating. In Waitlark, a referral counts after the friend confirms by email, and disposable addresses and obvious loops are filtered out.
Where do I find my own numbers?
Your waitlist tool shows signups per day and how many people confirm. For the share rate, count the confirmed people who brought at least one friend. For friends per sharer, divide the signups through referral links by that number. Measure over a week or two, then run the calculator again.
Is what I type stored anywhere?
No. The calculator runs in your browser, and nothing you type is sent to us or anyone else.

Another question? Chat with us.

Read and try next

ReferralsA share link per person. Every confirmed friend moves them up.Bot protectionCloudflare Turnstile, rate limits, disposable-email blocking and referral checks.DashboardSignups per day, confirmation rate, sources, answers and the full list.GuideReferral waitlistHow a referral waitlist works: a share link per person, moving up the line and rewards at milestones, and how to keep it fair and free of fake signups.GuideBuild a waitlistHow to set up a waitlist before you launch: write the promise, put up one page, keep the signup short, send the first emails and plan launch day early.GuideLaunch day invitesOpen up to your waitlist on launch day: invite in batches, pick who goes first, send one-time links or codes and know what to check before the next batch.Free toolUTM link builderTag the links you share for a launch: presets for six launch channels, clean lower-case values and a copy button.Free toolLaunch email templatesThe four waitlist emails with your product, name and launch date filled in: confirmation, welcome, update and invite, in plain text and HTML.Free toolLaunch countdown generatorA countdown timer for your launch page: date, time zone, words and colours with a contrast check, as one snippet with no external files.Free toolOpen Graph previewSee how a link looks on Google, X, LinkedIn, Facebook, Slack and in chats, check title length and image size, and copy the meta tags.Free toolEmail list cleanerFind invalid, duplicate, mistyped and disposable addresses in a pasted list or a CSV, and download the clean list. Nothing is uploaded.
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Join the waitlist for Waitlark. We invite people in small groups, and waitlist members get the early-bird price.

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