Check Broadband Speed by Postcode: What Your ISP Won't Tell You

Why ISP Coverage Checkers Do Not Tell the Full Story

Every major ISP has a coverage checker on their website. Enter your postcode, and they will tell you what speeds are available. The problem is that each checker only shows that ISP's own infrastructure. BT's checker will not tell you about CityFibre's full-fibre network running down the same street. Virgin Media's checker will not mention the Openreach FTTP upgrade scheduled for next quarter. And none of them will tell you about the mobile coverage situation — whether you can make a phone call indoors or whether your 4G will drop to 2G the moment you step inside.

Ofcom, the UK communications regulator, publishes the most comprehensive broadband and mobile data through its Connected Nations programme. This data covers every UK postcode with information from all operators, not just one. It shows actual median speeds (not 'up to' marketing figures), technology availability by provider, and mobile coverage from all four networks. But Ofcom publishes this as large datasets and static reports — there is no public API for querying a specific postcode.

The gap between what ISPs advertise and what Ofcom measures can be significant. An ISP might advertise 'superfast broadband available' for a postcode, which technically means 30Mbps+ is available from at least one provider. But if only one provider offers superfast and the rest are limited to ADSL at 10Mbps, the competitive picture is very different from what the headline suggests.

For anyone moving house, signing a business lease, or evaluating a property investment, independent broadband data from the regulator is more useful than any single ISP's self-reported coverage. The Digital Connectivity endpoint aggregates Ofcom's data with additional sources to give a complete picture in one call.

How to Check Broadband and Mobile Coverage

The fastest way to check connectivity is our free Postcode Profiler tool. Enter a postcode and the area profile includes broadband speed ranges and technology availability as part of the overall area data. This gives you an immediate sense of whether a location has decent internet before you investigate further.

For detailed connectivity data, the Digital Connectivity API at /api/v1/connectivity/{postcode} returns comprehensive broadband and mobile coverage information. The response includes average download and upload speeds, superfast and ultrafast availability percentages, ISP coverage breakdown, mobile coverage by operator for both 4G and 5G, full-fibre (FTTP) availability, and a Digital Readiness Score.

The endpoint supports three depth levels. Summary depth costs 4 credits and returns the Digital Readiness Score, headline speeds, and FTTP availability. Standard depth costs 10 credits and adds per-operator mobile coverage, ISP competition data, and digital exclusion risk factors. Full depth costs 20 credits and includes planned infrastructure upgrades, detailed speed percentiles, and community-level comparisons.

The alternative is to check multiple sources manually. Ofcom's interactive coverage maps require separate lookups for fixed broadband and mobile. Each mobile operator has its own coverage checker. ThinkBroadband provides crowdsourced speed data but with variable coverage. The API combines all of these into a single structured response with consistent fields, making it practical to compare postcodes systematically rather than one at a time.

Broadband Technology Types and What They Mean for Speed

UK broadband is delivered over several technology types, and the technology available at your postcode determines your realistic speed ceiling. Understanding these technologies is essential for interpreting broadband data.

ADSL (Asymmetric Digital Subscriber Line) runs over copper telephone lines from the exchange to your premises. Maximum speeds depend on line length — properties close to the exchange might get 17Mbps, but those more than 3km away may see only 2-5Mbps. ADSL is the baseline technology available at almost every UK postcode but is increasingly inadequate for modern usage.

FTTC (Fibre to the Cabinet) runs fibre-optic cable from the exchange to the street cabinet, then copper from the cabinet to your premises. This hybrid approach delivers 30-80Mbps for most connections, with the copper 'last mile' still limiting speeds. FTTC is marketed as 'superfast' broadband and is available at approximately 96% of UK premises.

FTTP (Fibre to the Premises), also called full fibre, runs fibre-optic cable all the way to your property. This delivers symmetric speeds of 100Mbps to 1Gbps or more, with no degradation over distance. FTTP availability has grown rapidly — from approximately 15% of UK premises in 2020 to over 55% by 2026 — but gaps remain, particularly in rural areas.

The API response distinguishes between these technologies and shows which are available at the queried postcode. If FTTP is available, the broadband situation is excellent regardless of other factors. If only ADSL is available, speeds will be limited and the postcode will score lower on the Digital Readiness Score. The availability of FTTC represents a middle ground that serves most households adequately but may struggle with heavy multi-device usage.

Mobile Coverage by Operator

Mobile coverage in the UK varies significantly by operator and by whether you are indoors or outdoors. The four major networks — EE, Three, O2, and Vodafone — each have different infrastructure footprints, and coverage at a specific postcode can range from excellent on one network to non-existent on another.

The API returns 4G and 5G coverage status for each operator at the queried postcode, with separate indoor and outdoor assessments. Indoor coverage is the more demanding metric because building materials attenuate mobile signals. A postcode with strong outdoor 4G from all four operators but weak indoor coverage from two of them presents a very different experience depending on whether you work from home.

5G coverage remains concentrated in urban centres and is expanding gradually. The API shows current 5G availability by operator, which is useful for businesses evaluating 5G-based fixed wireless access as an alternative to wired broadband in areas with limited FTTP.

Coverage gaps are particularly relevant for rural properties, new-build developments (which may not yet appear in operator databases), and properties in topographic dips or valleys where line-of-sight to masts is limited. The API data comes from Ofcom's Connected Nations reports, which are based on operator-submitted coverage predictions validated by Ofcom's own drive-testing programme.

For businesses, mobile coverage affects not just personal communications but increasingly operational technology — delivery tracking, mobile payments, IoT sensors, and remote monitoring all depend on reliable mobile data. A warehouse in a 4G blackspot from the chosen operator creates operational problems that a postcode check would have identified in advance.

The Digital Readiness Score Explained

The Digital Readiness Score is a proprietary rating from 0 to 100 that synthesises broadband and mobile data into a single measure of how well-connected a location is. Higher scores indicate better connectivity across all dimensions.

The score is calculated from five weighted factors. Broadband speed carries the highest weight at 30%, measuring average download speeds against national benchmarks. A postcode with 200Mbps average download scores well; one limited to 8Mbps ADSL scores poorly. Full fibre availability accounts for 25% — this forward-looking metric rewards areas where FTTP infrastructure exists, recognising that full fibre provides a higher speed ceiling and more reliable service than copper-based alternatives.

Mobile 4G and 5G coverage contributes 20%, aggregating coverage predictions from all four operators for both indoor and outdoor scenarios. A postcode with strong indoor 4G from all operators and 5G availability scores higher than one with outdoor-only coverage from two operators.

ISP competition accounts for 15%. Postcodes served by multiple broadband providers with overlapping infrastructure offer consumers more choice and typically lower prices. A postcode where only a single provider operates has less competitive pressure on speed and pricing.

Digital exclusion risk contributes the final 10%. This factor incorporates demographic data — areas with older populations, higher deprivation, and lower qualification levels face greater risk of digital exclusion even when infrastructure is available. It is a social dimension that pure infrastructure metrics miss.

Score bands: 0-25 indicates Poor connectivity (likely ADSL-only, limited mobile), 26-50 is Below Average (FTTC available but no FTTP, patchy mobile), 51-75 is Good (FTTP available, strong 4G), and 76-100 is Excellent (FTTP, competitive ISP market, 5G available).

Using Connectivity Data for Decisions

For individuals moving house, a connectivity check before signing a lease or making an offer can prevent months of frustration. Working from home on an 8Mbps ADSL connection while your partner streams video and children attend online classes is a qualitatively different experience from doing the same on 300Mbps FTTP. The API check costs 10 credits at standard depth — a fraction of a penny — and takes less than a second.

For businesses choosing premises, connectivity is a site-selection criterion alongside rent, transport links, and labour market. A logistics company needs reliable mobile data for fleet tracking. A software company needs low-latency broadband for development and deployment. A retail business needs stable connectivity for card payments and inventory systems. The Digital Readiness Score provides a single number that captures all of these dimensions, enabling rapid comparison across candidate locations.

Property developers and investors use connectivity data to assess the digital infrastructure of an area. A new residential development in an area with FTTP availability can market broadband speeds as a selling point. An area without full fibre may face buyer resistance from remote workers who now treat fast broadband as a requirement rather than a bonus.

At scale, the API enables portfolio-wide analysis. A property investment fund evaluating 200 locations can query all of them in minutes and rank by Digital Readiness Score. A telecommunications company planning network expansion can identify underserved postcodes — those with high population density but low connectivity scores — as priority targets for infrastructure investment.