What this Christmas cake calculator does

Every year it's the same problem. You've got a recipe written for one size of tin, and a cupboard full of tins that are a completely different size. Maybe you inherited your gran's 9in tin and the recipe is for 8in. Maybe you're making a small cake for two people instead of a family-sized one. Either way, doing the maths by hand is fiddly, and getting it slightly wrong means a cake that's too wet in the middle or burnt round the edge.

This Christmas cake calculator does that maths for you. Tell it the tin you're using (round or square, in inches or centimetres), or how many portions you need, and it works out the exact weight of currants, sultanas, raisins, butter, flour, eggs, almonds and spices for that size, plus how long to bake it, how much marzipan and icing to buy, and a brandy feeding plan that counts down to Christmas Day. You can run it with our own Classic recipe, which follows a standard UK rich fruit cake chart, or switch to Mary Berry's published Christmas cake recipe if that's the one you know and trust.

How to use the calculator, step by step

Everything happens in the box above this post. Here's what each control actually does, so nothing feels like guesswork.

Classic recipe or Mary Berry's recipe?

Both options make a proper, boozy, long-keeping rich fruit cake, but the ratios are different enough that it's worth knowing what you're choosing between. Mary Berry's recipe uses a bit less currant, sultana and raisin per tin size and makes up for it with extra dried apricots, and her finished cake is wrapped in a noticeably thicker layer of marzipan and icing than the general chart calls for. Here's how the two compare for an 8 inch round tin.

If you've made Mary Berry's Christmas cake before and want the exact same cake, just scaled, pick her option. If you'd rather follow a slightly lighter-fruit, more standard bake, the Classic option is the one to use. Either way, every other part of the calculator, the bake time, the feeding countdown, the method, works the same.

Christmas cake tin size and bake time chart

One of the most useful things this Christmas cake calculator does is work out bake time for you, because a smaller cake simply needs less time in the oven than a large one, and getting that wrong is how cakes end up dry at the edges or raw in the middle. These times are for a fan oven at 120°C and are what the calculator uses behind the scenes for a round tin.

These numbers are a sensible starting point, not a guarantee. Every oven runs slightly differently, so always start checking with a skewer from around twenty minutes before the time shown, and keep checking every ten to fifteen minutes after that until it comes out clean.

Round tin or square tin?

A square tin holds noticeably more mixture than a round tin with the same number of inches across, because the corners add extra area that a round tin simply doesn't have. As a rough rule, a square tin takes roughly as much mixture as a round tin that's about an inch bigger across. So an 8in square tin needs close to what a 9in round tin needs, not what an 8in round tin needs.

You don't need to remember that rule or do the sum yourself. Just tap "Square" in the calculator and enter the size written on your tin, and every ingredient weight, the bake time, and the marzipan and icing amounts are adjusted for a square tin automatically.

How much marzipan and icing you'll need

Buying too little marzipan halfway through covering a cake is a genuinely annoying way to lose an afternoon, so this is one of the things worth checking well before the day you plan to ice. These are the Classic recipe amounts the calculator works from, for a cake finished in marzipan plus royal icing.

Fondant icing uses roughly the same weight as the marzipan figures above. If you choose Mary Berry's recipe instead, expect to buy noticeably more marzipan and icing than this table shows, since her finished cake is wrapped in a thicker, more generous layer. The calculator's Baking tab always shows the exact figure for your chosen tin, shape, recipe and icing style, so you never need to eyeball it from a chart like this one.

When and how often to feed your cake

Feeding is what turns a dense fruit cake into a properly moist, matured Christmas cake, and it's also the step people forget to plan for. Once the cake is completely cool, you pierce it a few times with a skewer and spoon over a little of your chosen spirit, then repeat every week or two right up until you cover it with marzipan and icing, at which point the feeding stops because you don't want to soak through the covering.

The calculator works this out for you on the Feeding tab. Based on your baking day, it counts the days left to Christmas, works out how many feeds reasonably fit in that window, usually between one and six, and lays out a specific date for each one, along with the date marzipan and icing should go on, roughly a week before you plan to serve the cake. If you're baking very close to Christmas, it'll tell you honestly that there isn't really time to feed it properly, rather than inventing a feeding plan that doesn't make sense.

Frequently asked questions