What we used to say, and why we stopped
The advice on this page until September 2026 was: LinkedIn runs a second-price auction on sponsored messaging, so bid $5, $10, even $100 — you will only pay just above the next bidder, typically $0.50 to $1.00, and the high bid guarantees you win the one-message-per-person slot. It was the standard advice in the category and we ran accounts on it.
Then we measured it. Kiin Labs' 2026 study of every sponsored messaging campaign in accounts connected to Kiin Intelligence — 315 accounts, 2,166 campaigns, 22.6 million sends, $7.85M, 8 September 2025 to 7 September 2026 — compared each account's highest-bid campaign against its lowest-bid campaign, in the same account, where the bids were at least 1.5× apart. 119 accounts qualified.
| Highest-bid campaign ÷ lowest-bid campaign, same account (n=119) | Ratio | 95% CI | High bid better in |
|---|---|---|---|
| The bid itself | +192% | [+150%, +233%] | — |
| Cost per send | +80% | [+56%, +110%] | 23 of 119 |
| Cost per open | +77% | [+47%, +108%] | 28 of 119 |
| Cost per lead (n=64) | +44% | [+8%, +64%] | 21 of 64 |
| Open rate | +0% | [−3%, +4%] | 60 of 119 |
| Lead rate | +22% (ns) | [−14%, +62%] | 44 of 77 |
| Form completion | +1% (ns) | [−8%, +11%] | 23 of 46 |
Within account, bid to cost per send correlates at r = +0.62 and is positive in 86% of the 86 accounts with enough campaigns to test. Bid to open rate: r = −0.09. Bidding higher bought nothing except a higher price. The second-price mechanism is real — the median campaign pays 62% of its bid — but it protects you far less than "you pay $0.50 whatever you bid" implied. If you bid $3, you pay about $1.86. If you bid $0.30, you pay about $0.19.
What actually sets cost per send
| Driver | Effect on cost per send | Evidence |
|---|---|---|
| Your bid | r = +0.68 across 1,572 campaigns; elasticity 0.53 — bid +10% → cost per send +5.3%; explains 35% of the variance on its own | ★★★ |
| Audience size | 50,000+ vs under 15,000, same account: −24% [−38%, −14%], cheaper in 56 of 68 | ★★ |
| Retargeting vs cold | +5% [−1%, +17%], ns | |
| Uploaded list vs cold | +7% [−2%, +28%], ns (lead-form campaigns: +21%*, because advertisers bid up for named accounts) | |
| Multi-step vs single message | −15% [−31%, +2%], ns | |
| Seniority filter | +6%, ns | |
| Month of the year | Index 98–107 every month — no seasonality | ★★ |
| Weeks since launch | Drifts up about 13% by weeks 6–8 | ★★★ |
Cost per send is the bid you type and the size of the audience. Not who is in it, not the month, not the format. And cost per send is 55% of what decides cost per lead — more than open rate (2%), form completion (13%) or whether openers click into the form (38%) combined with each other.
The bid bands
Cross-campaign medians by the bid the advertiser set:
| Bid per send | Campaigns | Open rate | Cost per send | Cost per open | Cost per lead |
|---|---|---|---|---|---|
| Under $0.30 | 273 | 46.0% | $0.16 | $0.37 | $65 |
| $0.30–$0.50 | 370 | 40.0% | $0.27 | $0.71 | $155 |
| $0.50–$0.80 | 361 | 41.7% | $0.38 | $0.90 | $170 |
| $0.80+ | 568 | 39.5% | $0.72 | $1.86 | $421 |
Open rate is flat across the bands. The campaigns bidding under $0.30 are not getting worse inventory; they are getting the same inventory for a fifth of the price. The cheapest ten accounts in the panel, at $13 a lead, bid a median $0.35; the dearest ten, at $1,776, bid $1.03 — and the dearest ten also ran smaller audiences (17,000 vs 97,000) and more list targeting (31% vs 0%), which is the rest of the story.
What about delivery?
The argument for bidding high was always delivery: LinkedIn shows a member one sponsored message per 45 days, so if you lose the auction you do not send at all. That constraint is real. What the data shows is that it is not binding for most advertisers most of the time: campaigns bidding under $0.30 still delivered 273 qualifying campaigns' worth of sends with the highest open rate of any band. Delivery is a function of audience size more than bid — the same account's 50,000+ audiences cost 24% less per send than its sub-15,000 ones — so the fix for a campaign that cannot spend is a wider audience, not a higher bid.
If a campaign genuinely cannot deliver at a low bid — a tiny retargeting pool in a contested US market — raise the bid in steps and watch cost per send, knowing each +10% costs about +5.3%. That is a decision to pay more for a specific audience, made on purpose. It is not the default.
How Kiin bids sponsored messaging now
- Manual bidding, always. Maximum delivery hands the bid to LinkedIn.
- Start under $0.30 per send. Raise only if the campaign cannot spend its daily budget after a week, and raise in small steps.
- Widen the audience before raising the bid. 50k+ audiences pay 24% less per send in the same account.
- Ignore LinkedIn's recommended bid. That part of the old advice survives.
- Judge the campaign on cost per lead or cost per booked meeting, never on cost per send alone — but know that cost per send is 55% of the lead price.
- Expect no fatigue. Open rate by week since launch runs 109–115 (index, week 1 = 100) through week 8; the 45-day cap does the work. Cost per send drifts up ~13% by weeks 6–8.
Weekends: opens dip, leads don't
On feed ads (thought leader ads and sponsored content), weekends are the best click days: Saturday and Sunday impressions cost 1–4% less, engage the same, and click through 9–10% better than weekdays. On message ads, weekend opens read lower — Saturday 88, Sunday 93 against a weekday of 100 — but opens are dated when they happen, not when the message was sent, so part of that dip is Friday sends being opened on Monday. The measure that can't lag is leads per send by day of send, and that is flat: 0.16–0.17% every day of the week. Cost per lead sits within ±8% of the weekly mean (Tuesday $192, Saturday $223). Cost per send doesn't move by day at all; it's a bid.
Don't daypart weekends on either format. Which weekday is cheapest is an account-level question: our own case studies found Sunday cheapest in one account (a North American, UK and UAE audience — Sunday is a working day in the UAE) and Saturday dearest in another (US SaaS). Test it in your own account by day of send, not day of lead. The day-of-week chart and table are in chapter 13 of the conversation ads benchmarks.
What this does not tell you
The study cannot see message copy, subject lines or sender — none of the 8,673 creatives sync to the database — so nothing here is about what to write. On single-message versus multi-step conversation ads it calls a tie: +36% per lead for multi-step with an interval that spans zero, 20% fewer opens, 21% higher form completion, so pick by the offer rather than the price. The full study is LinkedIn Conversation Ads Benchmarks 2026; the thought leader ads study, which reached the same conclusion on bidding for feed ads (highest bid +128% per engagement), is here.