Please Note: Visa requirements and procedures are subject to change. Please visit the "Extension of Stay" section of the National Superintendency of Migration website of the government of Peru before finalizing your arrangements.
Following a procedural change in July 2008, tourists can no longer extend their “tourist visas” from within Peru. For most travelers (see "Do You Need a Tourist Visa for Peru?"), this “tourist visa” is the Tarjeta Andina de Migración, or TAM, a form obtained and completed at the border (unlike visas applied for and obtained prior to traveling).
If you want to extend your Tarjeta Andina, you will need to exit and re-enter Peru (a border hop) -- you cannot ask for an extension within Peru. If everything is in order and you haven't already been in Peru for too long, the border official will give you a fresh Tarjeta Andina when you re-enter the country. The number of days you are given, however, will depend on the mood of the border official and the number of days you had previously spent in Peru. This is where things can get complicated.
You Had Previously Spent Less Than 183 Days in Peru
If you were given 90 days on your Tarjeta Andina when you first entered Peru, extending your stay by means of a border hop shouldn’t be a problem. You can exit Peru at the nearest border and re-enter, in most cases, with a fresh TAM and 90 more days to spend in Peru. For more about border crossings, read Peru Border Crossing Basics.
You Have Already Spent 183 Days in Peru
Many border officials will give you the full 183 days on your TAM when you first enter Peru (especially if you ask for it). If you have already spent the full 183 days in Peru prior to a border hop, you may experience some difficulties re-entering Peru (see section on potential 2016 changes below).
Legislation regarding the 183-day maximum stay appears to be open to interpretation. Some border officials will adamantly insist that you can only spend 183 days in Peru each calendar year, in which case they may not want to let you re-enter Peru. Others will happily let you back in, giving you a fresh TAM and 90 more days in Peru (some will give you the full 183 days).
In my experience (and from various other reports), border officials on the Peru-Chile border are far more accommodating than on the Peru-Ecuador border. While I was applying for my resident visa, I needed to border hop to obtain enough time in Peru to complete my application. I had already spent 183 days in Peru. I crossed into Ecuador via the small border point near San Ignacio. When I tried to re-enter at the Macará-La Tina (Ecuador-Peru) border crossing, I was refused entry. The border official told me I had already stayed for the maximum time allowed and could not go back into Peru.
I finally convinced him to give me one month in Peru to complete my application. I re-entered Peru, but I knew I needed more than one month. I crossed into Chile a few weeks later; when I re-entered Peru the next day, I asked the border official for 183 days, which he happily granted without hesitation.
Logically, border officials should all abide by the same rules. This, however, is Peru. Some officials are ill-informed, while others may be looking for a bribe.
Alternatives to the Peru Border Hop
If you overstay your allotted time in Peru, you will have to pay a visa overstay fine when you exit the country. This fine is only US$1 per day (for each day spent in Peru after the expiration of your TAM). In many cases, paying the fine will be cheaper (and less hassle) than exiting and re-entering Peru.
Be careful, however, as you never know when a law might change in Peru (if the $1 was suddenly changed to $10, you might have a nasty shock; see final section below). You may not be able to pay the fine at some smaller border points, so always check before you exit the country.
Another alternative is to apply for a different type of temporary or resident visa before your TAM runs out. This is often a complicated and time-consuming process. The visa options available to you will depend on your situation but could include a work visa or marriage visa.
Potential Visa Regulation Changes in 2016
New visa regulations are set to be introduced in 2016. When exactly the precise details will be published -- and when any changes will actually be fully enforced -- remains to be seen. However, it's likely that border hopping beyond the 183-day limit will become far more difficult, or perhaps even impossible. There are also rumors about the one-dollar-a-day fine increasing to five dollars. So far, the full changes have not been officially released to the public.