Why does the interest look so large?

Because a long term multiplies it. 100,000 at 5 percent over 30 years costs 93,255 in interest, which is most of the amount borrowed again. Shortening the term raises the monthly payment and cuts the total sharply, which is the trade off the numbers here are for.

Does it handle an interest free loan?

Yes. The standard amortisation formula divides by the rate, so a zero rate makes it fail, and plenty of calculators return an error or a blank. An interest free loan is simply the amount divided by the number of payments, and that case is handled separately.

Is this financial advice?

This does arithmetic on the numbers you give it and nothing else. It is not advice, it does not know your circumstances, and it will not tell you whether something is a good idea.

Loan Repayment Calculator

Monthly payment, total repaid, and the interest.

Amount borrowed

Annual rate

Term in years

Monthly payment, total repaid, and the interest.

How to use it

Enter what you are borrowing. Currency symbols and separators are stripped.
Add the rate and the term. The annual rate as a percentage, and the term in years.
Look at the interest. Shown as an amount and as a share of what you borrowed.

When you would use this

A repayment figure is one formula, and the reason to have a page for it is what the formula does not tell you on its own. The monthly payment is the number people ask for and the total repaid is the number that matters. 100,000 borrowed at 5 percent over 30 years costs 193,255 to repay, which is 93,255 of interest, most of the loan again. Shortening the term raises the payment and cuts the total sharply, and seeing both figures side by side is what makes that trade off legible. One implementation detail worth mentioning. The standard amortisation formula divides by the interest rate, so a zero rate makes it divide by zero, and a surprising number of calculators return an error or a blank for an interest free loan. That case is handled separately here: no interest means the amount divided by the number of payments. No rates are looked up and nothing is sent anywhere. What you type stays in the page.

Questions

Why does the interest look so large?: Because a long term multiplies it. 100,000 at 5 percent over 30 years costs 93,255 in interest, which is most of the amount borrowed again. Shortening the term raises the monthly payment and cuts the total sharply, which is the trade off the numbers here are for.
Does it handle an interest free loan?: Yes. The standard amortisation formula divides by the rate, so a zero rate makes it fail, and plenty of calculators return an error or a blank. An interest free loan is simply the amount divided by the number of payments, and that case is handled separately.
Is this financial advice?: This does arithmetic on the numbers you give it and nothing else. It is not advice, it does not know your circumstances, and it will not tell you whether something is a good idea.