You can enter all the details in the Check detail split lines:
Principal
Interest
Amortize asset negative amount
Amortization expense positive amount
You can Memorize this Write Check. Set it Do Not Remind Me. Each Month, double-click, fill in the splits for Principal and Interest. The Amortization is the same every time, no need to make changes to this. The Payment amount is the same every time, too, so simply Double-click the Memorized transaction to rebalance Principal and Interest. Save and Close.
You can even set the Memorized Transaction to Automatic, Monthly, and Number Remaining. Save it with a "budgeted split" for Principal and Interest, which you will rebalance to match Actuals, each month. This is great for cash management for recurring payments, since it gives you the Banking amount automatically, and you refine the split details, later, at least before reconciling the Loan account to the lender's statement.
