The first 90 days with a new marketing agency isn't a process. It's a stress test. You won't know in 90 days whether the work will be excellent. That takes longer. What you'll learn is whether your assumptions about the business were right, and whether the agency is willing to tell you when they aren't.
The average client-agency relationship in 2025 now lasts roughly seven years, more than double the 3.2 years averaged in 2016 (ANA/4As, April 2025 report). The relationships that hit seven years all share something in common. They survived month four. The first 90 days is where that gets decided.
If you want a clean read on whether you've hired the right partner, the questions below are the ones to track. Not the deliverables in the proposal. The questions.
The short version
Average client-agency tenure is now 7 years, up from 3.2 in 2016 (ANA/4As, 2025). Clients without rushed reviews stay 8.1 years on average; clients who churn through frequent reviews drop to 3.8. Real B2B marketing impact arrives later than most teams expect: paid media in 30 to 60 days for first signal, content in 3 to 6 months (Mezzanine Growth, 2025). Meanwhile, 61% of B2B buyers prefer a rep-free buying experience (Gartner, 2025). The first 90 days is calibration, not delivery. Treat it that way.
Why does the first 90 days actually matter?
Because the agency relationships that work in year three almost always cleared a specific bar in month two. The 2025 ANA/4As client-agency tenure report found that clients without mandatory review periods stay with their agencies an average of 8.1 years. Clients with frequent reviews drop to 3.8 (ANA/4As, 2025). The decision to keep working together gets made early, even when nobody puts it on a calendar.
The first 90 days does two things that don't show up in the proposal. First, it tells you whether your business is briefable. Second, it tells you whether the agency can read your business back to you better than you can read it yourself. If both happen, year two is straightforward. If neither happens, you'll be running a search again before Christmas.
Most teams treat the first 90 days as a settling-in period. That's the trap. Settling in is what year two is for. What you're doing in the first 90 days is calibration: aligning what the agency assumed about your business with what is actually true, and aligning what you assumed about marketing with what the channels can actually deliver. Skip the calibration and the rest of the year is built on a wobble.
What should happen in week 1?
Less than the proposal made it sound, and more than your team will feel comfortable with. Week 1 is for access and alignment. Logins, analytics handovers, brand asset transfer, customer research, sales call recordings, three months of CRM data. The agency should be loading context, not delivering. If they're already running campaigns in week 1, that's a signal worth pausing on.
A practical week-1 checklist:
All analytics access (GA4, Search Console, Meta Business, LinkedIn Campaign Manager, your CRM, your ad accounts).
Brand library: logo files, fonts, colour palette, photography rights.
Sales recordings or transcripts: minimum five from the last quarter, ideally including two losses.
The most recent quarter of website analytics, with conversion paths.
Three customer interviews on the calendar (the agency leads, you join).
A working communication channel: shared Slack channel, weekly status, escalation path.
What you should not see in week 1: ad creative, campaign launches, social posts, big-ticket deliverables. The proposal sold you a launch. The work says: load first.
If the choice between agency, freelancer, and in-house is still part of your active decision, our guide on marketing agency vs freelancer vs in-house in the Netherlands
walks through the trade-offs we'd talk through with you on a discovery call.
What's actually happening in weeks 2 to 4?
The honest read. In a healthy partnership, the agency now tells you the things you didn't want to hear. Your positioning is fuzzy. Your offer is too broad. Your sales process drops the lead at the wrong moment. Your highest-traffic page is the wrong page. If they don't say any of this, that's the first red flag of the engagement.
This is the hardest stretch of the first 90 days because the calendar is full and the deliverables haven't started. It feels slow. It isn't. The work in weeks 2 to 4 is reframing: the agency is reading your business and telling you back what they see. 75% of B2B buyers now prefer to research independently before talking to a vendor (HubSpot, 2024). That means your positioning is doing more of the selling than your sales team is. If the agency can't sharpen the positioning in weeks 2 to 4, the rest of the year is built on whatever fuzz the buyer reads on the website.
What you should be doing during this stretch is holding the discomfort. The temptation is to say "let's just launch something" before the reframing is done. Don't. The launches that compound start with positioning that survives contact with the audience. Launches built on fuzzy positioning are expensive lessons.
What's actually happening in weeks 5 to 8?
First execution. The agency ships the first material thing: a landing page, a campaign, a piece of content. The metric to watch isn't the click-through rate. It's the conversation that happens when the first numbers come back. A real agency shows you wins and misses in the same email.
Most B2B paid media starts producing signals in 30 to 60 days; meaningful pipeline arrives in 60 to 120 days (Mezzanine Growth, 2025). Content marketing is slower: 3 to 6 months for early signals, 12 to 18 for meaningful pipeline. So the first numbers in weeks 5 to 8 are signal, not yet conclusion. They tell you the direction. They don't tell you the destination.
Watch how the agency talks about the numbers. Three patterns to flag:
The agency that overstates a small win in week 6 will overstate a small loss in week 12. Not a partnership.
The agency that buries a loss is the same agency that will bury the next three. Hard to fix later.
The agency that says "this didn't work and here's what we learned" in week 6 is the one you renew with.
In the engagements we've watched closely, the conversation in week 7 about a missed metric is more predictive of the year ahead than the proposal was. The numbers are smaller in week 7. The dynamic is identical.
What's actually happening in weeks 9 to 13?
First strategic adjustment. By now, signal has arrived. The agency proposes the first real shift: reallocating budget, changing the offer, narrowing the audience, switching the primary channel. This is when the partnership earns or doesn't earn the next quarter. A good agency comes with a recommendation and the data to defend it. A bad one comes with a deck.
Three or four weeks of execution data isn't enough to be definitive, but it's enough to be directional. The right move in week 12 is rarely "stay the course". It's almost always a calibrated shift: more budget into the channel that's working, less into the one that isn't, a sharper segment, a tighter offer. The agency that doesn't propose any adjustment by week 12 is the agency that won't propose one in month six either.
What this conversation should sound like: "Channel A is producing leads at €X cost per lead, but the lead quality is too low. We'd move 30% of that budget to Channel B based on the signal we've seen. Here's what we'd commit to seeing by month 5 if we do, and the risk if we don't."
What this conversation should not sound like: "Things are going well, here's a deck."
What should you know on day 90 that you couldn't on day 1?
Five things, none of which are in the proposal. Whether your positioning is sharp enough to win. Which channel actually fits your business. What your sales-to-marketing alignment really looks like under load. Whether the agency lead actually understands your business. Whether the partnership can argue productively. If three out of five are unclear at day 90, the next 90 are at risk.
A day-90 readiness check, in five questions:
Positioning. If the agency had to write a single sentence about your business right now, would it match what your buyers actually believe?
Channel fit. Out of the three to five channels you launched, which two is the agency willing to defend as your real growth lever for the next 12 months?
Sales handoff. When marketing-qualified leads land in sales, what percentage convert in the first 30 days? If you don't know, the alignment is the problem.
Lead understanding. In a 30-minute conversation, can the senior agency lead defend three non-obvious things about your business? If they can, you're partnered. If they can't, you're a client.
Productive argument. Has the partnership had a meaningful disagreement that resolved with a better answer than either side started with? If yes, that's the one that pays off in year two.
If you're saying yes to four or five, the 90 days went well. If you're saying yes to one or two, the next 90 are remedial.
What does healthy look like vs. what does trouble look like?
Healthy looks slow before it looks fast. Trouble looks fast before it looks slow. The agency that's busy in week 2 with discovery and quiet in week 6 with measurable pipeline is the one to bet on. The agency that's loud in week 2 and quiet in week 8 is the one to watch.
A short side-by-side. Healthy:
Asks more questions in week 2 than it answers.
Tells you in week 4 that something in your brief was wrong, and shows the data.
Reports a missed target in week 6 in the same email as a hit.
Proposes a budget reallocation in week 12 with a number attached to the recommendation.
Books month-6 strategy on the calendar in month 2.
Trouble:
Asks no clarifying questions, says "we've got this".
Validates everything in your brief without challenge.
Buries a missed target.
Goes silent for a week.
Sends a deck instead of a recommendation.
The agencies that protect a client's feelings in week 2 don't keep them past month 7. Honesty in week 2 is the most underrated retention tool in this industry, and the one the proposal stage almost never tests for.
What's different about the first 90 days in the Netherlands?
Three operational realities. Dutch holiday calendars eat working time in mid-July through late August, which is 4 to 6 working weeks of dead air if your 90-day window crosses summer. Many Dutch B2Bs run shorter sales cycles than US comparables but longer decision committees. International agencies working with Dutch clients should be set up for KvK-compliant invoicing on day one, not as an afterthought.
A few practical Netherlands-specific notes:
Plan around the calendar, not against it. A 90-day engagement starting in May effectively runs to early September because of summer. A 90-day engagement starting in October runs cleanly. Pick start dates with the calendar in mind.
Book Dutch customer interviews early. Customer research is harder to schedule in the Netherlands than agencies budget for. Three interviews in the first three weeks is a reasonable target. Six is ambitious.
Local proof beats global case studies. A Dutch B2B buyer responds better to a Dutch case study than to an American one, even if the American is more impressive on paper.
VAT and invoicing. If the agency is non-NL, ensure they understand BTW, KvK, and reverse-charge rules before signing. Lost time chasing this in week 4 is annoying. Lost time chasing this in week 11 is expensive.
If your wider question is whether the website you're handing the agency on day 1 is actually ready, our self-audit on whether https://sixtynine.agency/know-how/is-your-website-holding-your-business-back is the seven-check version we run before any new engagement.
Frequently asked questions
How long should onboarding actually take?
Two to three weeks of access, alignment, and discovery before any execution. According to the 2025 ANA/4As tenure report, clients without rushed reviews stay with agencies an average of 8.1 years versus 3.8 with frequent ones (ANA/4As, 2025). The teams that get onboarding right tend to be the ones that don't have to keep replacing the agency.
What if the agency seems too positive in week 4?
That's a signal, not a feature. Week 4 should include at least one hard conversation about something in the original brief that doesn't hold up. If everything is "going great" with no challenge, the agency is either avoiding a difficult truth or hasn't done the discovery work yet. Either way, push for the harder version of the conversation.
When is it actually too early to fire an agency?
Almost never inside the first 30 days unless they've broken trust. By day 60, you should have enough signal to know whether the partnership shape is right. Don't confuse early roughness with the wrong fit. B2B paid media shows signals in 30 to 60 days; pipeline takes 60 to 120 (Mezzanine Growth, 2025).
Should I sign a 12-month contract from day 1?
The honest answer is it depends on the work. Strategic engagements with positioning and brand work need at least 6 months to be fair. Execution-only retainers can run quarterly. The most balanced shape we see is a 90-day diagnostic phase followed by a 12-month strategic engagement, with quarterly review points.
What deliverables should I have by day 90?
At minimum: a documented positioning, a tested channel mix with first-quarter performance data, a working communication rhythm, a content or campaign baseline, and a strategic recommendation for the next 90 days that's defended with data. If three of those five are missing, the engagement isn't on track.
So, what should the next 90 days look like?
The first 90 days isn't where the work pays off. It's where you find out whether the work will pay off.
If you're at the start of those 90 days and want a sparring partner who'll tell you in week 2 what week 12 should look like, that's the kind of conversation we'd rather have over coffee than over a proposal. We'd rather hand you keys than invoices.
If that's the question you're trying to answer, let's talk.