High-Calorie Flapjack Recipe: 485 Calories a Square

Written by James Frost, founder of Flaming Phoenix. Updated October 2026.

A flapjack has about 430 to 465 calories per 100g, so a 60g square is roughly 260 to 280 calories and a 110g café-size bar is close to 490. This high-calorie flapjack recipe adds peanut butter, nuts and chocolate to reach 485 calories a square, with every ingredient added up below.

I'm James, and I make Phoenix Bars, high calorie bars for people who need to get more calories in than normal meals allow. Most flapjack recipes online chase "healthy", which usually means fewer calories. This one goes the other way on purpose. If you want fuel for the hills, a long ride or putting weight on, a light flapjack works against you, and the fix is denser ingredients, not a bigger portion you cannot finish.

How many calories are in a flapjack?

A flapjack has 433 to 465 calories per 100g on the UK labels I checked, so the size of the piece decides the total more than the recipe does.

• Holland & Barrett Oaty Flapjack: 433 calories per 100g (label on Ocado).
• Blackfriars Original Flapjack: 443 calories per 100g, so the 110g bar is about 487 calories (443 x 1.1).
• Flapjackery Traditional Flapjack: 465 calories per 100g.
• This recipe: 5,821 calories in 1,200g of raw mixture, which is about 485 calories per 100g, and also per square when you cut the tray into 12.

To get your own figure, multiply by weight. A 60g square of a 433 to 465 calorie flapjack is 260 to 279 calories (0.6 x 433 and 0.6 x 465). Cut this recipe into 16 smaller squares and each is about 364 calories. In that sense it is a homemade cousin of the Kalteen bars from Mean Girls, the fictional bars designed to help people gain weight.

Why are flapjacks so high in calories?

Flapjacks are high in calories because butter and sugar syrup make up a large share of the weight, and fat carries 9 calories per gram against 4 for carbohydrate and protein, as the NHS notes.

In this recipe the butter alone supplies 1,490 of the 5,821 calories, about a quarter. Add the peanut butter, nuts and chocolate and the fat-rich ingredients come to 3,578 calories (1,490 + 890 + 661 + 537), or 61% of the tray. The syrup, sugar and raisins add quick sugars and help the mix bind, and the oats give slower carbohydrate and the structure.

Ingredients (makes 12 squares, 485 calories each)

Calories are from UK labels on Ocado, checked in October 2026.

• 300g rolled or porridge oats: 1,107 kcal (Mornflake, 369 per 100g)
• 200g butter: 1,490 kcal (Ocado British salted, 745 per 100g)
• 150g golden syrup: 488 kcal (Lyle's, 325 per 100g)
• 100g soft light brown or light muscovado sugar: 392 kcal (Billington's)
• 150g smooth peanut butter: 890 kcal (Pip & Nut, 593 per 100g)
• 100g mixed nuts, roughly chopped: 661 kcal (Whitworths, no added salt)
• 100g raisins: 256 kcal (Ocado raisins; chopped dates would be 317)
• 100g dark chocolate chips: 537 kcal (Dr. Oetker, 45% cocoa)

The sum: 1,107 + 1,490 + 488 + 392 + 890 + 661 + 256 + 537 = 5,821 calories for the tray. Divided by 12 that is 485 calories a square; divided by 16 it is 364. Each of the 12 squares carries about 45g carbohydrate, 30g fat and 8.5g protein.

Method

Hands-on time is about 15 minutes, plus 20 to 25 minutes in the oven and at least an hour to cool and chill.

1. Heat your oven to 180C, or 160C fan, gas mark 4, and line a 20cm square tin with baking paper.
2. In a large pan over a low heat, gently melt the butter, syrup, sugar and peanut butter together until smooth. Do not let it boil; just melt and combine.
3. Take the pan off the heat and stir in the oats, nuts and raisins until everything is fully coated.
4. Let the mix cool for a couple of minutes, then fold in most of the chocolate chips so they hold their shape rather than melting away. Press the mixture firmly and evenly into the tin, and scatter the remaining chips on top.
5. Bake for 20 to 25 minutes, until golden at the edges. The centre will still look soft, which is right, because it firms up as it cools.
6. This next step is the one that matters. Cool the tray completely before cutting, ideally chilling it in the fridge for 30 minutes. Cutting flapjack while it is still warm is the main reason it crumbles. Once cold and set, cut into 12 squares.

How do you stop flapjacks falling apart?

Three things, and the third is the one most people skip. Use enough syrup and butter to bind, since a dry mix crumbles no matter what. Press the mixture down firmly in the tin so it sets as one slab. And cool it completely, ideally chilled, before you cut it. Warm flapjack has not set yet, so cutting it early is what turns squares into rubble.

Are flapjacks good for hiking, running and cycling?

Yes. British Cycling describes flapjacks as "a great mix of fast acting sugar, slower burning carbohydrates, some fat", and that mix suits food eaten on the move.

That mix is what people mean by a flapjack for sustained energy: sugar for now, oats for later. Most recipes written for the hills stop well short of this one; the Mountaintrails hikers' flapjack, for example, comes to about 440 calories a portion when cut into eight. Butter-rich flapjack softens on a hot day and firms up in the cold, so wrap squares individually and keep one in an inside pocket in winter. Eat it in bites, with a few sips of water, since it is dense. For shop-bought options, the guide to the best energy bars for hiking compares bars on calories per gram.

Are flapjacks good for bulking?

Flapjacks are useful for bulking when the problem is eating enough: one 485-calorie square covers most of the 300 to 500 extra calories a day the NHS suggests adults try when gaining weight.

The catch is protein. At about 8.5g a square, flapjack is mostly carbohydrate and fat, so pair it with a glass of milk or a yoghurt, or make the no-bake protein bar in my homemade high calorie bars recipe, which gives 25g protein a bar. If you would rather buy than bake, see my guide to picking a protein flapjack. Treat flapjack as a top-up between meals, not a meal in itself; the NHS guide to healthy ways to gain weight suggests smaller meals more often with snacks in between, and that is where a square fits. If you are bulking on purpose, the best high calorie foods for bulking covers the rest of the plan.

Variations

• Vegan: swap the butter for coconut oil or a vegan baking block, and check the chocolate (the Dr. Oetker chips are labelled suitable for vegans, with a may-contain-milk warning). My vegan flapjacks recipe is built that way from the start.
• Gluten free: use certified gluten-free oats, the only change needed here. The gluten free flapjacks guide covers cross-contamination and which ones to buy.
• Nut-free: drop the peanut butter and nuts and add extra sunflower and pumpkin seeds, plus a little more syrup or coconut oil to keep it binding. Recount the calories from your labels, as the total will fall.
• High carb: swap the 100g of nuts for another 100g of raisins. The tray drops to 5,416 calories (5,821 minus 661 plus 256), or 451 a square, but carbohydrate rises to about 50g a square, which suits racing better than bulking.
• Even higher calories: add another 50g of peanut butter for about 297 more calories in the tray, or 25 a square, or drizzle extra melted chocolate over the top once cooled.

For bar-shaped flapjacks rather than squares, and how to choose shop-bought ones, see my guide to flapjack bars.

If you would rather not bake

Baking a tray needs a kitchen, and it keeps for about a week. When that does not fit, for a multi-week expedition, a race drop bag or just a busy week, Phoenix Bars hold up to 557 calories in only 120g and keep for up to two years, so you can buy months ahead. You can also stir one into water to make porridge. Philip, who runs long fell routes, wrote in September 2026: "The Flaming Phoenix bars have now become the standard food for my long fell runs (15+ miles)." For the homemade route in bar form instead of a tray, see the homemade high-calorie bars recipe.

Frequently asked questions

Can you freeze flapjacks?
Yes. They freeze well for up to three months. Wrap them individually so you can grab one at a time, and they defrost in about an hour at room temperature or overnight in the fridge.

How long do homemade flapjacks keep?
About a week in an airtight container at room temperature. Made richer with nut butter and dried fruit, as this one is, they stay moist for several days rather than drying out. Keep them somewhere cool in summer, because the butter softens.

Are these flapjacks healthy?
They are calorie-dense on purpose, built for fuelling hard activity or gaining weight, not for cutting calories. Oats, nuts, peanut butter and dried fruit bring fibre and some protein, but at 485 calories and plenty of sugar a square, match them to that goal.

Is flapjack good for weight loss?
Not really. A 60g square of a shop flapjack is 260 to 280 calories, and one square of this recipe is 485, so it is easy to overshoot. If you are cutting calories, cut much smaller pieces or choose a lighter snack; this recipe is built for the opposite goal.

What is the best oat for flapjacks?
Rolled or porridge oats. Jumbo oats give a chunkier, looser texture, while standard rolled oats bind tighter and hold together better on the trail.

Related guides

Build the rest of your fuel from here: calorie-dense foods for the full ranking of what packs the most calories per gram, high-calorie snacks and best food for hiking for what else to carry, energy gel alternatives if you are moving away from gels, and how to gain weight if that is the goal.

About this recipe: I'm James, founder of Flaming Phoenix. I developed Phoenix Bars after about 150 conversations with ultra-endurance athletes, expedition people and people who struggle to eat enough, and they are rated 4.9 out of 5 from 391 reviews. This recipe is general information, not medical or dietary advice.

Sources: NHS, Fat: the facts; NHS, Healthy ways to gain weight; British Cycling, Fruit and mixed seed flapjack; flapjack labels from Holland & Barrett (Ocado), Blackfriars Bakery and Flapjackery; Mountaintrails, High energy flapjacks; ingredient labels on Ocado, October 2026: Mornflake oats, Ocado butter, Lyle's golden syrup, Billington's sugar, Pip & Nut, Whitworths mixed nuts, Ocado raisins, Whitworths dates, Dr. Oetker chocolate chips.