A regular mortgage loan almost always is set at 30 years. Besides the loan period there is also the duration of the interest fixed interval. You can vary from 1 year to 30 years. Interest fixed means that (annuity loan) your gross monthly cost levels will not change in this period,
The longer the interest fixed period you choose, the higher the interest rate level. And the longer the security you have that your monthly installments will not increase.
If you choose an initial period of 10 years you know that the interest rate is fixated and that only after 10 years you will be presented a new interest fixed rate proposal from your bank – against the rate of THAT TIME, so the rate could very well deviate from your current one, leading to a higher (or lower) monthly cost level for your next interest fixed period.