A student loan is not a loan in the ordinary sense
Every other calculator on this site answers the same question: here is a balance and a rate, how long and how much. A government student loan does not fit that shape, and using an ordinary loan calculator on one produces a number that is not merely imprecise but about the wrong thing.
In the United Kingdom the repayment is a share of income above a threshold. It has nothing to do with the size of the balance. Two people with the same salary and wildly different debts pay exactly the same amount each month, and the only thing the balance decides is whether anything is left when the term runs out. That is why the figure at the top of this page for most Plan 2 and Plan 5 borrowers is not a payoff date but a write-off.
In the United States the plan you are on decides almost everything. A fixed payment over a term set by the balance behaves like a normal loan. The income-based plan does not: its payment comes from a band of income, and interest that the payment fails to cover is not charged at all.
Why the balance can grow and it may not matter
On a United Kingdom plan with a large balance and an ordinary salary, the interest each month is larger than the repayment. The balance rises for years, sometimes for the whole term. Borrowers find this alarming and the alarm is misplaced: the amount repaid is decided entirely by income, and a balance that grows changes nothing except the size of the number eventually cancelled.
The practical consequence runs the other way from what people expect. Voluntary overpayments on a loan heading for write-off are money handed over for nothing, because the alternative was never paying it. The exception is the borrower who will clear the balance anyway, and the projection on this page is what tells the two apart. Look at whether the last row of the table reaches zero.
The newer American plan removes this problem by statute. Interest a payment does not cover is not charged, so the balance never rises, and a month whose payment barely touches the principal still takes a fixed amount off it. A borrower used to the plans this one replaced, where unpaid interest piled up and was capitalised, should read that twice.
Where the numbers come from
Everything except your own figures is read from the publication that sets it. The American rates come from the Department of Education's annual notice in the Federal Register, which is the document that announces them rather than a summary of one, and it reprints every year back to 2013. That is why this page asks which year your loan was first paid out: almost nobody remembers their rate and almost everybody remembers the year.
The United Kingdom thresholds and rates come from the Student Loans Company's own guidance on gov.uk. The repayment percentages, the write-off terms and the American statutory formulas are in the source list at the foot of the page, each pointing at the regulation or the guidance rather than at an article about it.