How We Score & Data Sources
ChaseSeasons surfaces data from several independent sources. This page explains how we turn that data into the season badges and rankings you see, what each source is, how we use it, and where its limitations lie.
How we score and sort destinations
Every destination gets a season label for each month, set from its price index and crowd index: Sweet spot (shoulder season — good weather without peak prices), Quiet season (off-season — cheapest, but often the weather is why) and Busy season (peak).
On the destinations page you can sort for the month of your trip:
- Best value — sweet spots first, then quiet season, then busy season. Within each, the lower price index for that month comes first, then the warmer destination.
- Warmest — highest average daily high for the month, with fewer rainy days breaking ties.
- Driest — fewest rainy days (days with at least 1mm of rain) for the month, with the warmer destination breaking ties.
Whatever the sort, a resort that is effectively closed that month (for example Sunny Beach in winter) always comes last: its low price index isn't a holiday you can book.
The price index is each destination's own scale, so it ranks months within a destination rather than comparing the cost of one destination with another. The school holiday premium shown alongside is always a range, explained in how we quote savings.
Temperature data — Meteostat and NASA POWER
The temperature band on each destination page shows, for every calendar month, the average daily high and average daily low over the last ten years. Our primary source is Meteostat, which redistributes observations from national weather services (including NOAA and Deutscher Wetterdienst) under the Creative Commons Attribution 4.0 licence. We use the weather station closest to each destination, so the figures reflect the place itself rather than a regional average.
Where no nearby station has a complete enough record, we fall back to NASA POWER, a public-domain dataset derived from satellite and model data on a half-degree grid. Grid data can run cooler than the coast for small islands and seaside towns, which is why we prefer station records.
The "Chance of rain" chart counts the average number of days per month with at least 1mm of precipitation — the threshold most climate summaries use to exclude trace or drizzle amounts. It uses the same window as the temperature band, and normally the same station, but a station's rain gauge can have gaps even when its temperature record is solid; where that happens we use NASA POWER's satellite precipitation estimate for rainfall specifically, while still using the station for temperature. Where neither source has reliable enough coverage, the page shows "not yet available" rather than an unreliable figure.
Method: daily maximum and minimum temperatures, averaged per calendar month over a ten-year window; a station is only used if every month has at least 60% of its days recorded. Rainy-day counts use the same window and the same 60% coverage bar, applied to precipitation readings.
Refresh: data is compiled once a year and published with the site — it is not a live feed
Attribution: Source: Meteostat (data providers include NOAA and Deutscher Wetterdienst); NASA POWER Project
Price indices
The price index shown on each destination (a normalised 0–1 scale) is independently researched from publicly available fare data and established seasonal patterns. It represents a relative price signal — how expensive a given month is compared to that destination's annual average — rather than a live price quote.
Important: Price indices are not real-time. They reflect typical seasonal patterns derived from historical data and are updated periodically (at least annually). Actual prices for specific travel dates will differ. Always check current prices on the booking platforms we link to.
The index is used to classify months as peak (typically ≥ 0.80), shoulder (0.45–0.79), or off-season (below 0.45), alongside the crowd index.
How we quote savings
The “17–29%” saving quoted on our homepage and booking badges comes from a published like-for-like price check by AllClear Travel (last updated June 2025). It compared the same 4-star package holidays for two adults, 7–10 nights with direct flights from London Stansted, on Jet2holidays, TUI and Expedia, departing mid-July versus mid-September 2025:
- Costa del Sol: 29% cheaper in September
- Crete: 26% cheaper
- Orlando: 20% cheaper
- Rome: 17% cheaper
We quote this because it is a UK, like-for-like comparison with a stated method. Its limits: four destinations, one year, one departure airport, and July against September only. Other published data points the same way but with different splits — KAYAK's 2025 analysis of US searches found autumn airfares to Europe 37% below summer, but international hotel prices only 10% lower, suggesting flights drive most of the saving.
Our own sampling: we are running a like-for-like price-sampling programme across our destinations, including the weeks either side of UK school holidays. When it has enough data we will publish the results and method here, and replace this figure with our own.
UK school holiday dates
There is no single national school calendar in the UK. Term dates are set by local councils in England and Wales, by each of Scotland's 32 councils, and by the Education Authority in Northern Ireland. For each region we store the dates that the large majority of councils use, and flag the known exceptions in the tooltip on the season calendar. We hold the current and next academic year and refresh every August.
- England & Wales — the common council pattern, cross-checked against Royal Borough of Greenwich, Norfolk and Coventry. Find your own council's dates via GOV.UK.
- Scotland — follows City of Edinburgh and Glasgow City Council, which most councils match. The February break is two days in Glasgow and the west but a full week in Edinburgh, the Lothians and Fife.
- Northern Ireland — Education Authority non-operational dates, which apply to almost all grant-aided schools.
Premium ranges: the “+15–30%” style badges show the typical uplift in package and accommodation prices during that school break compared with the surrounding non-holiday weeks. They are indicative ranges drawn from published fare patterns and our own price checks, not measurements for a specific destination or date. We will replace them with sampled figures per destination as our price-sampling programme matures.
Provisional dates: where a region has not yet published a year's dates, we show the expected pattern and mark it provisional in the tooltip.
Crowd data
Crowd index values (a normalised 0–1 scale) are derived from destination tourism authority reports, published visitor statistics, and known seasonal visitor patterns. They are not sourced from real-time footfall sensors or aggregated mobile data.
Like price indices, crowd indices reflect typical seasonal patterns and are updated periodically. Major events, natural disasters, or geopolitical changes may cause significant deviations from historical patterns. Always verify current conditions from official tourism authorities before travelling.
Destination photography
Destination photos come from Wikimedia Commons. Each one is checked individually before use for a licence that permits commercial use with no fee owed to the photographer — CC0, public domain, CC BY, or CC BY-SA. We don't use paid stock photo libraries. Full attribution for every photo in use is on the photo credits page.
Affiliate partner pricing
Where we show illustrative prices alongside booking links (e.g. “from £X per night in shoulder season”), these are shoulder-season estimates based on our independently researched price indices. They are not live quotes from booking platforms.
We have an active affiliate partnership with Expedia, and are evaluating additional partnerships including lastminute.com (via Awin), GetYourGuide, and Viator. Current prices are always displayed on the partner's own platform after you click through. For our affiliate disclosure, see Affiliate Disclosure.
Corrections and updates
If you spot data that appears to be incorrect or significantly out-of-date, please contact us at privacy@chaseseasons.com. We take data accuracy seriously — see our Editorial Standards for our corrections policy.