Ask ten owners how they set their ad budget and eight will say some version of "what felt safe." A round number. Whatever is left over at the end of the month. What the last agency asked for.
That is how you end up with a budget too small to learn anything, or too big for a business that has not fixed its tracking yet. Both waste money. One just wastes it slower.
Here is a better method. It takes about ten minutes, and the only inputs are numbers you already know or can look up.
The percent-of-revenue rule, and where it breaks
The most repeated rule says small businesses should spend 7 to 8 percent of revenue on marketing. That guidance comes from an SBA planning worksheet for businesses under $5 million in revenue, and the same worksheet admits budgets swing from 2 percent to 20 percent depending on the stage of the business.1
Big companies land in the same range. Gartner's 2026 CMO survey put marketing budgets at 7.8 percent of revenue, and its 2025 survey found paid media took about 30.6 percent of that budget.2 Most of those respondents run companies with more than $1 billion in revenue, so treat it as context, not a target.
The rule is a fine sanity check. It is a poor way to set an ad budget, for one reason: it has nothing to do with what a customer costs you. A dental practice and a pizza shop with the same revenue should not spend the same on ads, because a new patient and a new pizza order are worth very different amounts.
The formula: start with customers
Work backward from the result you want. Four numbers get you there.
- Customers you want per month. Be specific. "Ten new roof replacements," not "more business."
- Your close rate. Out of every 100 leads, how many become paying customers? If you do not know, 20 to 30 percent is a common starting guess for local services.
- Leads needed. Customers divided by close rate. Ten customers at a 25 percent close rate means 40 leads.
- Cost per lead. Use your own history if you have it. If not, use an industry benchmark from the table below.
Then multiply: leads needed times cost per lead equals your monthly ad budget. WordStream's budget guide uses the same core math: average cost per lead times the number of leads you want.3
2026 cost-per-lead benchmarks
WordStream and LocaliQ analyzed 13,474 U.S. search campaigns from April 2025 to March 2026. Across all industries, the median search campaign paid $5.42 per click and $66.69 per lead, with an 8.18 percent conversion rate. Cost per lead actually fell year over year for the first time in five years.4
| Industry | Google cost per click | Google cost per lead | Facebook lead-ad cost per lead |
|---|---|---|---|
| Home and home improvement | $8.33 | $90.92 | $42.95 |
| Legal services | $9.87 | $131.63 | Not reported |
| Dental | $8.00 | $72.97 | $61.56 |
| Physicians and surgeons | $4.76 | $40.04 | $32.14 |
| Health and fitness | $6.17 | $67.36 | $27.11 |
| Beauty and personal care | $4.62 | $39.25 | $50.91 |
| Real estate | $3.22 | $102.51 | $13.74 |
| Restaurants and food | $2.05 | $30.57 | Not reported |
Google figures: WordStream/LocaliQ 2026 search benchmarks. Facebook figures: WordStream 2026 Facebook lead-ad benchmarks. All medians.4,5
Two things jump out. First, Facebook leads usually cost less than Google leads. WordStream's 2026 data put the median Facebook lead-ad cost at $27.39.5 Second, cheaper is not the same as better. A Google lead typically searched for you on purpose. A Facebook lead raised a hand while scrolling. Close rates are often different, so compare cost per customer, not cost per lead.
Platform minimums you cannot ignore
Every ad platform learns from conversions. Starve it of data and it guesses. That sets a practical floor under your budget, no matter what the formula says.
- Google Ads: Google recommends judging Smart Bidding over a period with at least 30 conversions, such as the last 30 days.6 At the home improvement median of $90.92 per lead, that is roughly $2,728 a month before the numbers mean much.
- Meta: An ad set usually exits its learning phase after about 50 results in a week.7 Below that, costs run higher and results swing. Fewer, larger ad sets beat many small ones.
- TikTok: Campaign daily budgets must exceed $50 and ad group daily budgets must exceed $20.8 That puts the floor near $608 a month per ad group, before you pay for any creative.
If the formula gives you a number below these floors, you have two honest options. Narrow the goal to one service and one audience, or start with a channel that needs less data to work, such as Local Services Ads or local SEO.
Three worked examples
A roofing contractor on Google
Goal: 10 new jobs a month. Close rate: 25 percent. That is 40 leads. At the home improvement median of $90.92, the budget is about $3,637 a month. If an average job brings in $9,000, the ad cost per job is about $364. That math works.
A med spa on Meta
Goal: 30 new clients a month. Close rate on booked consults: 35 percent. That is about 86 leads. At a $40 cost per lead, the budget is roughly $3,440 a month. Watch the learning phase: 86 leads spread across four ad sets is too thin, so run one or two.
A product brand testing TikTok
Goal: learn which videos sell before scaling. Budget: $50 a day per campaign across two campaigns, about $3,040 a month, plus the cost of 10 to 20 new videos. On TikTok, creative volume matters more than budget in the first 60 days.
Where small budgets leak
When we audit small accounts, the budget is rarely the real problem. The leaks are.
- Broken tracking. Form fills counted twice, calls not counted at all. The platform optimizes toward the wrong thing, and you judge the channel on fake numbers.
- No negative keywords. Paying for "roofing jobs" and "plumber salary" searches.
- Too many campaigns. Ten campaigns at $10 a day each teach the algorithm nothing. One at $100 a day teaches it plenty.
- Stale creative. The same four ads for six months. On Meta and TikTok, fatigue raises costs every week.
- Sending traffic to the homepage. A slow page with no clear next step wastes the click you paid for.
Fix those first and the same budget often buys twice the leads. That is why every Ads Arsenal engagement starts with tracking, not spending.
The short version
Decide how many customers you need. Divide by your close rate. Multiply by what a lead costs in your industry. Check the result against each platform's learning floor. Then protect that budget from the leaks above.
If you want a second set of eyes on the numbers, our Google Ads, Meta Ads, and TikTok Ads teams will audit your account for free and tell you what we would spend, and where we would cut.
Sources
- U.S. Small Business Administration, SBA Ascent, "Create Your Marketing Plan" worksheet, 2020.
- Gartner, 2026 CMO Spend Survey (May 2026) and 2025 CMO Spend Survey (May 2025).
- WordStream, "The Complete Guide to Google Ads Budgets," updated April 2026.
- WordStream by LocaliQ, "Google Ads Benchmarks 2026," May 2026. 13,474 U.S. search campaigns, medians.
- WordStream by LocaliQ, "Facebook Ads Benchmarks 2026," September 2026. Leads-objective campaigns, medians.
- Google Ads Help, "About Smart Bidding" and "About Target CPA bidding," 2026.
- Meta Business Help Center, "About the learning phase," 2026.
- TikTok Ads Manager Help Center, "About Budget," July 2026.
