How accurate is a 5-day forecast for planning a day out?

Good enough to plan around, if you know which parts to trust and when. Here is what the forecasters themselves say, what it means for a day out, and how Perfect Day uses it.

Updated 16 September 2026.

The short answer

A five-day forecast gets the weather right about nine times in ten. Seven days out it is about four in five. Ten days out it is a coin toss. Those are not our figures; they are the US National Oceanic and Atmospheric Administration's, and the pattern is the same everywhere: the atmosphere is changing all the time, so a forecast is less reliable the further ahead it reaches.

For planning a Saturday, that means: pencil it in a week out, decide three or four days out, and glance once more the night before. Most of the regret in weekend planning comes from doing one of those at the wrong distance — committing on a ten-day forecast, or waiting for certainty that a forecast can never give.

In the forecasters' own words

NOAA puts it plainly: A seven-day forecast can accurately predict the weather about 80 percent of the time and a five-day forecast can accurately predict the weather approximately 90 percent of the time. And then: However, a 10-day—or longer—forecast is only right about half the time. The reason, in the same breath: The atmosphere is changing all the time, so those estimates are less reliable the further you get into the future. NOAA NESDIS, “How Reliable Are Weather Forecasts?”

The UK's Met Office describes the trend rather than the number: our four-day forecast is now as accurate as our one-day forecast was 30 years ago. Forecasts have got better fast, and keep getting better; the limit is not the forecasters, it is the weather. Met Office, “How accurate are our public forecasts?”

What “accurate” means for a day out

Those percentages describe the forecast as a whole. Different parts of it age at different speeds, and the parts that matter for a day outside are not the ones the headline is about.

• Whether the day is broadly fine or broadly wet is the most durable thing in a forecast. A dry, settled Saturday five days out usually stays dry and settled.
• Temperature holds up well several days ahead; being two or three degrees off is common and rarely changes a plan.
• Timing is the fragile part. Whether the showers arrive at eleven or at three, whether the wind drops by the afternoon, whether the cloud breaks before or after lunch: these firm up in the last two or three days and not before.
• How it will feel depends on dew point as much as temperature, and almost no forecast leads with it. Two days with the same number on the thermometer can be a lovely afternoon and a sticky, tiring one.

So a forecast can tell you a week ahead that the weekend looks worth keeping free, and only a few days ahead which hours of it are the good ones. A tool that plans days out has to respect both distances.

Why Perfect Day stops at ten days

Perfect Day watches sixteen days ahead, because that is as far as the data goes, but it will only tell you about a day within the next ten. Past that, the weather models stop agreeing with one another often enough that a message would be a guess wearing a confident tone, and one wrong promise costs more trust than ten right ones earn. The marks past the ten-day line are there on your screen to look at; they are never sent to you.

Inside ten days, a day is not judged on a symbol. Every hour in your chosen window is checked against the conditions you set — temperature or how it feels, dew point, wind and gusts, rain chance, cloud, UV — and the day only counts if enough of those hours pass in a row. Five weather models are fetched and averaged hour by hour, so one model's optimism never becomes a promise on its own. The whole thing is re-run every three hours.

When a promised day falls through

It happens; that is what “about nine in ten” means. When a day we told you about stops qualifying as the forecast moves, you get one more message that says so — Thursday fell through. The forecast moved; it is now cloudier than you asked for — and the day stays on your screen for a day, greyed, with the reason. No excuses, no exclamation marks. We would rather tell you a day is gone than let you find out standing in a car park.

How to plan a Saturday around a forecast

1. Seven days out: notice, do not commit. If the weekend looks settled, keep it clear. If it does not, make no plans that depend on the weather.
2. Three or four days out: decide. Timing is firming up. Pick the day — Saturday or Sunday — and the half of it.
3. The night before: check the hours. Where the showers sit, when the wind drops. Shift by an hour or two if you need to.
4. The morning of: look out of the window. Nothing beats it.

Perfect Day does the first two of those for you, and tells you once, on the day it becomes clear. The last two are yours, and they are the good part.