"SOI" gets searched for a lot of unrelated reasons that have nothing to do with performance marketing - people looking up statements of interest, statistics-of-income tax data, or store operating income. In affiliate and CPA marketing, SOI means something narrow and specific, and getting the definition right matters because it directly changes what an offer pays and how it converts.
The TrafficSigma team put this glossary entry together to answer the affiliate-marketing meaning of SOI plainly - what single opt-in actually requires from a lead, how it compares to DOI, and where SOI offers tend to show up.
What does SOI mean in affiliate marketing?
In performance marketing, SOI stands for single opt-in, and the single opt-in meaning is deliberately narrow: a lead converts the moment they submit one action - almost always an email address, or a short form with a name and email - with no second step required. There's no confirmation email to click, no verification code to enter, no waiting period. The affiliate network's tracking pixel fires as soon as the form is submitted, and that's the conversion.
This is worth stating explicitly because the broader web use of "SOI" (statement of interest, schedule of investments, statistics of income) is a completely different concept. This guide is scoped only to SOI in affiliate marketing - the lead-generation and CPA/CPL model.
Three category types structure how SOI sits inside the wider lead-gen landscape:
- Single opt-in (SOI): one action, instant conversion, no verification step.
- Double opt-in (DOI): the same initial form, plus a required confirmation click (usually via email) before the lead counts.
- CC Submit / trial offers: a step beyond both - the user enters payment details, which raises payout further but also raises the bar for conversion.
SOI sits at the volume end of that spectrum: easiest to convert, lowest friction for the user, and - as the next section covers - the lowest payout per lead as a direct tradeoff.
SOI vs DOI: how the extra step changes payout
The mechanical difference between SOI vs DOI is a single confirmation step, but that one step changes the entire economics of the offer.
With SOI offers, a user fills in a form once and the lead counts immediately. Nothing verifies that the email is real, active, or that the person meant to submit it - which means volume is high but a meaningful share of leads are low-quality: fake addresses, typos, or users who just clicked through to reach the next page. Networks price that risk into the payout, so SOI offers typically pay less per lead than the same offer run as DOI.
With DOI offers, the same initial form is followed by a mandatory confirmation - usually a "click to verify" link sent to the submitted email. That extra click filters out invalid addresses and low-intent submissions before the advertiser ever pays for the lead, which is why DOI commands a meaningfully higher payout per conversion: the advertiser is buying a verified contact, not just a form submission.
The practical tradeoff for an affiliate is volume versus payout, not a straightforward "better or worse":
- SOI: higher conversion rate, lower payout per lead, faster to test at scale - often recommended as a starting point for affiliates new to CPA/CPL offers because the funnel has fewer drop-off points.
- DOI: lower conversion rate (some users never complete the confirmation click), higher payout per lead, and a cleaner lead file - better suited once an affiliate has a proven funnel and wants to shift toward quality over raw volume.
A campaign that looks profitable on SOI can look unprofitable if the same traffic is pushed into a DOI version of the offer without adjusting expectations for the conversion drop from that extra step, and vice versa: a DOI offer's higher payout can still underperform an SOI offer on total revenue if the traffic source doesn't have the intent to complete a confirmation click.
The compliance tradeoff that goes beyond payout. Because SOI never verifies that the person submitting the form actually owns and controls that email address, lists built this way carry meaningfully higher spam-complaint and deliverability risk than DOI lists once an advertiser starts emailing them. That's not just a data-quality issue - jurisdictions with strict consent requirements for marketing communications, GDPR in the EU being the most commonly cited example, generally treat double opt-in as the standard way to document that a subscriber actually consented, since the confirmation click is itself evidence of consent that a single form submission can't provide. Affiliates and advertisers running SOI offers into consent-sensitive markets should treat that as a real compliance consideration, not just a lead-quality one.
Scale your sweepstakes offers with TrafficSigma's high-converting traffic!Where SOI offers are most common
SOI offers show up wherever the advertiser's goal is building a large contact list quickly and the cost of a lower-quality lead is manageable:
- Sweepstakes and prize-draw offers - one of the largest verticals for SOI, where users submit an email for a chance to win a gift card, gadget, or cash prize. Volume matters more than immediate lead quality here, which is exactly what SOI is built for.
- Newsletter and content sign-ups - publishers and list-building advertisers who plan to warm up leads over time via ongoing email, rather than needing a verified subscriber on day one.
- Finance and lead-gen verticals - simple contact-info submissions (loan interest, insurance quotes) where the advertiser's own sales team does the qualification work after the lead comes in, rather than relying on the opt-in step to pre-qualify it.
- Mobile content and app-install adjacent offers - quick single-field submissions used as a low-friction entry point before a deeper funnel.
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Comparison table: SOI vs DOI at a glance
| Model | User action required | Conversion speed | Typical payout | Lead quality | Best for |
|---|---|---|---|---|---|
| SOI (Single Opt-In) | One form submission (e.g., email) | Instant | Lower | Lower - unverified | High-volume testing, sweepstakes, newsletters |
| DOI (Double Opt-In) | Form submission + confirmation click | Slower (depends on confirmation) | Higher | Higher - verified | Proven funnels, quality-sensitive advertisers |
Choosing between SOI and DOI for your offer
The choice between SOI and DOI comes down to what an advertiser is actually optimizing for: SOI trades payout for volume and speed, DOI trades volume for a verified, higher-value lead. Neither model is universally "better" - the right one depends on whether the offer's funnel can absorb unverified leads or needs the confirmation step to protect quality.
Once the offer economics are clear, the next variable that decides whether an SOI or DOI campaign is actually profitable is the traffic behind it - volume alone doesn't help if it isn't reaching users likely to complete even a single form. That's the part TrafficSigma's 220+ GEO network and granular targeting are built to solve.
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For more on the sweepstakes vertical where SOI offers are especially common, see What Is Sweepstakes? How the Sweepstakes Casino Model Works for Affiliates in 2026.
