Pay Off the Mortgage or Invest? The Answer Changes Over Time

“Mort­gage at 4%. Ex­pected market return 7%. Easy de­ci­sion, right?” The com­par­i­son looks simple be­cause it places two per­cent­ages side by side. One is a con­trac­tual bor­row­ing cost. The other is an un­cer­tain in­vest­ment out­come. Your bal­ance sheet, cash needs, taxes, and re­tire­ment date com­plete the de­ci­sion.

Com­pare equal cash flows

Sup­pose you have €100,000 avail­able and owe €100,000 on a 30-year mort­gage at 4%. You can repay with­out a penalty, the monthly pay­ment is about €477, and you assume a con­stant 7% annual in­vest­ment return. Ignore tax, fees, inflation, and volatil­ity for this il­lus­tra­tion.

The mort­gage pay­ment fol­lows the stan­dard for­mula:

$$M = P\frac{i(1+i)^n}{(1+i)^n - 1}$$

Compare two paths:

• Keep the mort­gage, invest €100,000 on day one, and sub­tract the re­main­ing mort­gage bal­ance from the in­vest­ment ac­count.
• Pay off the mort­gage, then invest the €477 monthly pay­ment that dis­ap­pears.

Under the smooth 7% as­sump­tion, in­vest­ing first finishes ahead by about €39,500 after 10 years, €108,000 after 20 years, and €229,000 after 30 years.

The result fol­lows from the as­sump­tions. The model gives in­vest­ments 7% while the mort­gage costs 4%. Change the in­vest­ment return to 3% and the payoff path leads by about €32,500 after 30 years. A small change in the return as­sump­tion can re­verse the answer.

Add liq­uid­ity and un­cer­tainty

Paying €100,000 into the house gives you more home equity and less ac­ces­si­ble cap­i­tal. Home equity cannot pay an emer­gency in­voice. You may be able to borrow against the prop­erty later, but a future lender will set the terms at that time.

An in­vest­ment ac­count gives you more access, but the bal­ance can fall when you need it. Time re­duces some market risk, yet a three-year hori­zon de­mands more cau­tion than a 25-year hori­zon. Match the return as­sump­tion to the asset al­lo­ca­tion you would ac­tu­ally hold.

Keep your emer­gency re­serve out­side both strate­gies. A split ap­proach can also make sense: repay €50,000, invest €50,000, keep cash, or make sched­uled over­pay­ments while in­vest­ing the rest.

Size the cash re­serve firstWork out how much ac­ces­si­ble cash your house­hold needs before com­mit­ting sur­plus cap­i­tal to debt re­pay­ment or in­vest­ing.→

Re­cal­cu­late for re­tire­ment

A mort­gage cre­ates a debt bal­ance and a re­cur­ring cash outflow. Both belong in the re­tire­ment model.

Sup­pose you retire with €800,000 in­vested, an €80,000 mort­gage bal­ance, a €10,000 annual mort­gage pay­ment, and €30,000 of other annual spend­ing. Keep­ing the mort­gage re­quires €40,000 from the port­fo­lio, a 5% first-year with­drawal. Paying it off leaves €720,000 in­vested and €30,000 of spend­ing, a 4.17% with­drawal from the smaller port­fo­lio.

The second path lowers the re­cur­ring with­drawal burden but also re­duces liquid assets. Com­pare taxes, loan in­ter­est, ex­pected re­turns, and se­quence risk before choos­ing.

A mort­gage pay­ment also af­fects a FIRE target. At a 4% with­drawal rate, €10,000 of annual mort­gage spend­ing adds roughly €250,000 to a 25× target while the pay­ment con­tin­ues. Map the re­main­ing pay­ments by year. Five years of pay­ments and a per­ma­nent hous­ing cost do not create the same prob­lem.

Re-run the choice as your life changes

At 35, liq­uid­ity and a long in­vest­ment hori­zon may matter most. Near re­tire­ment, re­mov­ing a fixed pay­ment can reduce the amount your port­fo­lio must supply after a market fall. The loan bal­ance, pay­ment count, in­ter­est rate, and your cash needs also change over time.

Compare at least two dates: re­tire­ment and the final mort­gage pay­ment. In­clude the two end­point strate­gies and a par­tial re­pay­ment sce­nario. Fignis can place the mort­gage, in­vest­ment ac­count, re­tire­ment date, and spend­ing path on the same time­line.

Use the rate com­par­i­son as a first cal­cu­la­tion. Make the final choice from the whole bal­ance sheet.

Put hous­ing inside the wider planCom­pare hous­ing costs, cash use, flex­i­bil­ity, and in­vest­ment op­por­tu­nity cost across the full own­er­ship de­ci­sion.→ Check the loan cash flowsEs­ti­mate pay­ments, re­main­ing debt, and total in­ter­est before com­par­ing the mort­gage with an in­vest­ment path.→