Christmas dinner timing calculator

For an unstuffed 5kg whole turkey, the Food Standards Agency says allow 40 minutes per kg in an oven preheated to 180°C (160°C fan), which is 200 minutes, or 3 hours 20 minutes. Then rest it for 30 to 45 minutes under foil. Always follow the pack label first, and check the thickest part reaches 75°C with a meat thermometer. The calculator also adds a little spare oven time in case the bird needs longer.

The Food Standards Agency says to allow around 10 to 12 hours per kg in the fridge, on the bottom shelf, covered, in a dish that catches the drips. A whole turkey typically takes 3 to 5 days, and a 6 to 7kg bird could take as much as 4 days. Never defrost it at room temperature, and check there are no ice crystals in the cavity before you cook it. If the packaging gives defrosting instructions, follow those.

BBC Good Food says to rest a turkey for 30 to 45 minutes before carving, in a warm place, tented loosely with foil. It will not go cold, and the meat becomes juicier and easier to carve. Resting also frees the oven for the roast potatoes and trimmings.

Check the thickest part of the bird, between the leg and the breast, with a probe thermometer. Food Standards Scotland says it should reach 75°C or above, with no pink meat and clear juices. The Food Standards Agency lists 70°C held for 2 minutes and 75°C held for 30 seconds as equivalent ways to be sure it is cooked. BBC Good Food gives 75°C to 80°C for poultry on its roast timer. If a reading is low, return it to the oven for 10 to 15 minutes and test again.

You can, but treat it as a food safety job. The Food Standards Agency and Food Standards Scotland say to cool cooked turkey as quickly as possible, within one to two hours, then cover it and refrigerate it. When you reheat it, make sure it is steaming hot all the way through, and do not reheat it more than once. Many people prefer to cook on the day for the best texture. The calculator is built around cooking on the day.

BBC Good Food's roast potato recipe uses about 50 minutes in a hot oven, with the potatoes boiled for about 2 minutes first and then steamed dry for at least 15 minutes. This calculator starts the par-boil about 25 minutes before the turkey comes out and puts the potatoes in just after, so they finish as the turkey is carved. You can also par-boil the day before and chill them, as BBC Good Food suggests.

The Food Standards Agency advises cooking stuffing in a separate roasting tin, not inside the bird. A stuffed turkey takes longer and may not cook through to the middle. If you do stuff it, weigh the bird with the stuffing in, use a thermometer, and tick 'stuffed' on the calculator, which adds extra spare time and a warning.

BBC Good Food, passing on advice from British Turkey, says cook a crown at 190°C (170°C fan, gas 5): for under 4kg allow 20 minutes per kg plus 70 minutes, and for over 4kg allow 20 minutes per kg plus 90 minutes. A 2.5kg crown works out at 2 hours. Crowns often come with their own instructions on the pack, so use those if you have them.

Do not wash it: the Food Standards Agency says this spreads germs onto your hands, worktops and utensils. Cook from frozen only if the manufacturer's instructions on the pack say that bird can be. Most frozen turkeys need to be fully defrosted first, because a bird that is still partly frozen can cook unevenly and leave harmful bacteria alive.

BBC Good Food's size guide says 2 to 2.5kg serves 4 to 6, 3kg serves 6 to 7, 3.5kg serves 7 to 8, 4 to 4.5kg serves 8 to 10, 5 to 5.5kg serves 10 to 12, and 6 to 6.5kg serves 12 to 15. If you put in the number of guests, the calculator compares it with that guide.