Deep Dive: TikTok vs. Instagram – Where Should Your Brand Invest?

For years, Instagram dominated social marketing. Then came TikTok — a platform that didn’t just change the format, but the fundamentals of how audiences discover, engage, and buy.

By 2025, UK marketers are asking a crucial question: where should brands focus budget and energy — TikTok or Instagram? The answer isn’t one-size-fits-all, but data shows that for growth, conversion, and cultural impact, TikTok is pulling ahead.

Let’s break down the platforms head-to-head across engagement, advertising performance, creator ROI, and social commerce.

1. Audience: Where the Growth Really Is

TikTok’s rise has been explosive. The platform now reaches 24.8 million UK users aged 18+, nearly half the adult population — and it’s growing fastest among the 25–44 age group. Instagram remains larger overall (32M+ UK users), but its engagement growth has stalled, particularly among younger demographics.

Metric (UK 2025)TikTokInstagramMonthly Active Users24.8M32.1MAvg. Monthly Usage49 hours8 hoursTop Age Bracket18–3425–44Engagement Rate~4.0%~0.6%% Users Following Brands62%78%% Users Discovering New Products88%44%

Takeaway:
Instagram still wins for reach — especially for established audiences — but TikTok wins for time and attention. The average TikTok user spends over six times longer in-app than on Instagram, creating far more chances for your content to be seen, shared, and remembered.

2. Algorithm & Content Discovery

TikTok: Interest Graph

TikTok’s “For You Page” doesn’t depend on who you follow. Instead, it uses an interest graph — surfacing content based on what you watch, not who you know. This gives every post a chance to go viral, whether you have 50 followers or 500K.

Instagram: Social Graph

Instagram’s algorithm still prioritises existing connections. While Reels have improved discovery, it’s harder for smaller creators or new brands to break through without paid promotion.

Example: When Somerce launched a new skincare brand, early TikTok videos gained 80K organic views in 48 hours. The same content on Instagram Reels peaked at 3K. TikTok’s organic reach remains 10–30× higher on average.

3. Advertising & Paid Media ROI

Both platforms offer strong ad tools, but performance data shows clear differences in cost and creative efficiency.

MetricTikTok AdsInstagram AdsAvg. CPM (UK)£4–6£8–12Avg. CTR1.3–1.8%0.7–1.1%Best FormatSpark Ads (boosted creator posts)Reels AdsCreative Refresh RateEvery 7 daysEvery 14–21 daysPerceived AuthenticityHighModerate

TikTok’s Spark Ads — which amplify existing creator content rather than polished brand assets — consistently outperform static creative. For Somerce clients, TikTok CPMs average 35–50% lower than Meta’s, while ROAS is typically 1.4× higher when paired with affiliate content.

Instagram remains strong for remarketing and retention, but it’s increasingly a pay-to-play platform. Organic reach for brand accounts has dropped below 5%, while TikTok’s algorithm still regularly surfaces unpaid content from business profiles.

4. Social Commerce: The Deciding Factor

TikTok’s in-app shopping ecosystem is its biggest differentiator in 2025.
The seamless integration of TikTok Shop — product tagging, affiliate sales, and Live shopping — makes discovery and purchase frictionless.

Instagram has introduced in-app checkout in select markets, but adoption lags behind, and UK users often still exit to a website.

FeatureTikTok ShopInstagram ShoppingIn-app checkoutYes (fully live in UK)Limited (US only)Affiliate marketplaceYes – 200K+ UK creatorsNoLive shoppingFully integratedPilot-stage onlyAvg. Shop Conversion Rate6–10%1–3%Seller Count (UK)200K+N/A

Why it matters:
TikTok is not just entertainment — it’s an e-commerce engine. Live events now drive millions in daily GMV, while affiliate creators function as micro-sales reps. Instagram, in contrast, remains an inspiration and validation channel, not a purchase destination.

5. Influencers vs. Creator Sellers

Instagram built the influencer era — glossy feeds, curated partnerships, and branded posts.
TikTok has evolved it into creator commerce — a model where influencers become sellers, not endorsers.

On TikTok:

• Creators earn commission via TikTok Shop’s affiliate programme.
• Posts are discovery-first, not aesthetics-first.
• Authenticity beats perfection.

This shift has given rise to what Somerce calls “Creator Sellers” — people who blend entertainment with real sales performance.

Example:

• Glow For It built a 500-strong creator community via Somerce, producing short, unscripted Lives. Their affiliate-driven revenue grew 5× in 90 days.
• P.Louise, another Somerce client, achieved £2M in a single TikTok Live day, fuelled by creators promoting exclusive bundles and pre-tagged Shop listings.

Instagram still delivers brand-building influence; TikTok delivers transaction-driven results.

6. Content Performance and Longevity

TikTok content burns faster — but it also spreads faster.
A TikTok video can hit its viral peak within 48 hours, then fade. Instagram content has a slower, steadier curve.

TypeTikTokInstagramContent lifespan3–5 days7–14 daysViral potentialExtremely highModerateShelf life for adsShort (high refresh)Longer (lower engagement)

That’s why content velocity is key on TikTok.
Agencies like Somerce produce 10–20 new creative assets per week per brand — mixing UGC, educational clips, and Live recaps — to stay in sync with algorithmic trends. On Instagram, three to five high-quality posts per week can still maintain reach.

7. Brand Building vs. Direct Response

It’s not either/or — it’s where each platform excels.

• TikTok: Culture, virality, lower-funnel conversions
• Instagram: Visual storytelling, loyalty, retargeting

Brands launching or scaling should use TikTok for growth and Instagram for credibility.
The ideal flow?

“See it on TikTok → Trust it on Instagram → Buy it in TikTok Shop.”

When combined strategically, this omni-social loop drives the strongest ROI.

8. Somerce Insight: Where to Invest in 2025

After managing TikTok ad spend for over 50 UK brands, Somerce’s data points to a clear split:

• 60–70% of paid social budget should now go to TikTok (top-of-funnel discovery, Shop conversions, Live events)
• 20–30% to Meta/Instagram (remarketing, brand presence)
• 10% to experimentation (YouTube Shorts, Pinterest, X)

This balance aligns with performance metrics showing TikTok’s lower CPMs and higher creator-driven ROI, while retaining Instagram for credibility and retention.

9. Future Outlook

TikTok’s dominance will grow as its search, Shop, and AI content recommendation expand. Instagram’s strength will remain in community and long-term brand equity.

For UK brands, the smart strategy is not to pick a winner but to align each platform to its natural strength:

• TikTok for momentum and conversion
• Instagram for identity and trust

10. Final Verdict

Brand GoalBest PlatformWhyRapid reach & viralityTikTokHigh discovery, low costDirect salesTikTok ShopBuilt-in checkout & Live sellingCommunity buildingInstagramFollowers & DMs drive loyaltyAesthetic storytellingInstagramVisual-first brand presenceLong-term CRMInstagramIntegrated remarketing toolsCultural relevanceTikTokTrend-led, fast-moving audience

Summary:
TikTok is where audiences decide what’s cool.
Instagram is where they validate that decision.

If your goal in 2025 is growth, sales, and cultural traction, your brand should be born on TikTok — and mature on Instagram.

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