My credit card and bank account rarely agree on the date for when I pay it off1. Since I added balance assertions for bank account transactions, I need the transaction in my ledger to match what the bank thinks, otherwise the balance assertions would start to fail.

The skew is not normally more than a couple of days, and could be corrected by changing the date for just one of the two postings. But the skew is not very important, and altering the posting date could be used for something more useful.

date warping credit card repayments

My credit card bills land halfway through the month, so February's bill covers transactions between January 15th and February 14th. I pay off the bill in full each month using Direct Debit. The credit card company consider the bill paid immediately, but they don't actually draw it until the end of the month (Jan 31 in the running example). This means the payment transaction for a given month lands halfway through the period covered by the next month's bill.

The credit card bill itself shows the payment date at the end of the month but presents the transaction "warped" right to the start. This is actually useful, because it means the balance is zero for the first purchase on the bill.

The credit card data in CSV form has the repayment transaction at the date it occurred, not warped to the start of the period. When I import this into HLedger, the credit card account balance for each new transaction does not match the statement right up to the point of the repayment, half way through. This makes spot-checking that the imported data matches the statement a bit more awkward.

So, I have started "warping" the payment transaction to the start of the billing period, just like the credit card statement does:

2022-12-31  pay credit card
  asset:bank    £ -500
  liabilities:credit card  ;  date:2022-12-15

I can then spot-check the transactions in HLedger after import, in particular the final one, and the final account balance, and then write a manual balance assertion when I'm finished.

I'd quite like to automate the adjusted posting date, too, but I haven't figured out how to do that just yet.

date warping for refunds

Another thing I've found "date warping" useful is for marrying up refunds with their related purchase. Imagine I spent £200 on some shoes in late January, but returned most of them in early February:

2023-01-25  buy some shoes. hedging on the size
  liabilities:credit card    £ -200

2023-02-05  return the ones that don't fit
  liabilities:credit card    £  150

If I look at how much I've spent on shoes per month, it looks odd: £200 in January (although ultimately I only spent £50), and £-150 in February.

Balance changes in 2023-01-01..2023-02-28:

$ hledger bal -Mt expenses:shoes
                ||   Jan     Feb 
 expenses:shoes || £ 200  £ -150 
                || £ 200  £ -150 

By "warping" the refund's posting to the expense account to the purchase date, how much I ultimately spent on shoes is more properly reflected:

2023-02-05  return the ones that don't fit
  liabilities:credit card    £  150
  expenses:shoes  ; date:2023-01-25

resulting in

$ hledger bal -Mt expenses:shoes
Balance changes in 2023-01-01..2023-02-28:

                ||  Jan  Feb 
 expenses:shoes || £ 50    0 
                || £ 50    0 

I suppose whether you'd want to do this is a matter of taste.

  1. Amazon rarely agrees with my bank on when we've paid for things either. For other reasons, Amazon is a beast to tackle in another blog post.