One bill, several loans underneath
Student loan statements often group several separate loans under one bill. Each loan has its own balance and its own interest rate, even when the payment shows up as a single number.
A combined total hides which loans are the expensive ones. A loan at 7% and a loan at 4% can sit side by side on the same statement, building interest at very different speeds. The calculator treats each loan as its own line, so the rates and balances stay visible.
Listing loans one by one also changes the math, not just the view. Averaging the rates and treating everything as one balance can give a different interest total than tracking each loan on its own, because the balances shrink at different speeds.
Where the extra money goes
Every loan gets its required payment each month. In the calculator, the extra amount goes to one focus loan at a time, following the order chosen. That could be highest rate first, smallest balance first, or a custom order. The avalanche and snowball pages explain those two orders in depth.
Rate matters because of how interest builds. An extra $100 on a 7% loan avoids about 58 cents of interest the next month. The same $100 on a 4% loan avoids about 33 cents. Small numbers, but the difference repeats every month the money stays off the balance.
How a loan servicer splits an extra payment across several loans can vary. The calculator follows the order set on the page and puts the extra on one loan until it is gone.
What happens when one loan is paid off
Once a loan reaches zero, its required payment doesn’t disappear from the plan. It joins the extra amount and moves to the next loan in line. The total paid each month stays the same, but more of it goes toward principal.
That is why the per-loan payoff months often look like a staircase. The first loan takes the longest relative to its size. Each later loan is hit with a bigger monthly amount and tends to fall faster. Not sure which loan to start with? The which debt to pay off first page ranks the possible orders by interest and months.
What the calculator assumes
The results come from a straight monthly model. Each month, interest is the balance times the rate divided by 12, then the required payment, then the extra.
Rates and payments are held steady at the values entered until each loan is paid off. Some loans carry variable rates, and a rate change would shift the results. Running the calculator again with updated numbers shows the new picture. All dates and interest totals are estimates, not quotes from a servicer.
The calculator also assumes every required payment is made each month and that no loan is paused or changed along the way. It covers the payoff math only. Program rules and repayment plan options are outside what it models. Each result shows the payoff month for every loan, the order they are cleared, and the total interest for the whole group.