does interest payment on loan stay the same if I pay early
The typical case would be - as you expected - that the interest goes down equally dramatically, and you would pay much less interest. Note that that does not remove your obligation to pay the full 1000 every month - even though you could argue that you are 90 months ahead in paying, you still need to deliver 1000 a month, until it is fully paid. Some mortgages are made differently - they do not allow that. Basically, if you pay a large amount at once, it is considered a 'pre-payment' for the next x month. As a result, you are now x months ahead (and could stop paying for that much time), but your interest stays high. The latter type 'protects' the bank against 'losing' the interest income they already planned for. As a balance, those type of mortgages are typically slightly cheaper (because the bank is in a better position). You did not specify a country; in Germany, typically all mortgages are of the second type; but - you can get 1.35% mortgages... In the US, most are the first.  You need to check which type you have, best before you pay a large amount. In the latter case, it is better to invest that money and use it to pay off as soon as you reach the threshold; in the first case, any extra payoff is to your advantage.