Where do I put computations for reusable cells?

Question

In my view controllers, a lot of my cellForItemAt methods have computations in them. In the following example, I get the amount, image, and balanceAtDate and pass them into my view:

func collectionView(_ collectionView: UICollectionView, cellForItemAt indexPath: IndexPath) -> UICollectionViewCell {
        
        let cell = collectionView.dequeueReusableCell(withReuseIdentifier: SummaryCell.cellId, for: indexPath) as! SummaryCell
        
        let amount = filteredTransactions[indexPath.row].transactionAmount

        let image = UIImage(named: filteredTransactions[indexPath.item].transactionCategory!.categoryName)

        let balanceAtDate: Double = realm.objects(Transaction.self).filter("transactionDate <= %@", transactionResults[indexPath.item].transactionDate).sum(ofProperty: "transactionAmount")

        cell.configure(with: image, and: amount, and: balanceAtDate)
        
        return cell
    }

It has come to my attention that I shouldn't make any computations or calculations in cellForItemAt because it is called for every cell and it will slow down the application.

I create 3 constants: amount, image, and balanceAtDate. Do I need to put all three somewhere else, or just the balanceAtDate?

Where, then, do I put a computation that requires the indexPath.item to get something like the balanceAtDate?