Google Ads minimum viable spend in the UK 2026 is £1,500–£3,000/mo per channel for statistical signal within 60 days. Below that, you're guessing. Realistic monthly budgets: local services £1,500–£3,000; SMB B2B £3,000–£8,000; mid-market SaaS £5,000–£15,000; e-commerce D2C £3,000–£30,000; enterprise B2B £15,000–£50,000. London CPCs run 30–50% above UK averages.
Step 1: Define target customer acquisition cost (CAC). For SaaS: 1/3 of LTV is the rule of thumb. For e-com: gross profit per order minus payback period costs.
Step 2: Estimate conversion rate from click to customer. Average: B2B SaaS 1–3% click-to-lead, 5–15% lead-to-customer. E-com 1–4% click-to-purchase.
Step 3: Multiply: CPC £5 / conversion rate 2% = £250 cost per lead. Need 10 leads/mo = £2,500 budget. That's the floor.
Step 4: Add 30% buffer for testing and ongoing optimisation. Start at £3,250/mo for above example.
London commercial-services CPCs are punishingly high because thousands of agencies bid on each other. 'PPC agency london' itself costs £18–£35 per click. 'Web design london' £8–£16. 'Marketing agency london' £10–£22.
Long-tail and borough-specific terms are 50–80% cheaper. 'PPC agency Shoreditch' £3–£8. 'web design Battersea' £3–£6. Long-tail wins on cost; loses on volume.
Local services (plumber, dentist, gym): £1,500–£3,000/mo. CPCs £1–£6. CPL £30–£120.
SMB B2B services: £3,000–£8,000/mo. CPCs £3–£12. CPL £100–£400.
Mid-market SaaS: £5,000–£15,000/mo. CPCs £5–£20. CPL £200–£500.
E-commerce D2C: £3,000–£30,000/mo. CPCs £0.50–£3. CAC 5–15% of AOV at break-even ROAS.
Enterprise B2B: £15,000–£50,000/mo. CPCs £8–£30. CPL £500–£1,500.
Spend less when: you've maxed out best-converting keywords, additional spend is diminishing returns, organic SEO is taking over the same query.
Spend more when: ROAS is >3x and scaling, you have unspent CAC budget, competitor activity is intensifying, seasonal demand is up.
Don't spend at all when: landing page conversion <1% (fix landing page first), CAC > 6-month payback (fix product or pricing first), in market with no buying intent (build content first).
"Start at minimum viable. Run 60 days. Cut keywords with no conversion. Double down on winners. Add 20–30% budget. Repeat. Avoid one-shot 'big launch' budgets — data needs cycles to optimise."
Most agencies charge 8–18% of media spend on % models, or £449–£3,999/mo flat retainer. Flat fees align incentive (agency doesn't push you to spend more for higher fee).
Below £1,500/mo media spend, DIY is fine (Google's tools are decent). £1,500–£10,000/mo: specialist freelancer or agency. Above £10,000/mo: dedicated agency or in-house team.