You want to know whether buying or continuing to live in rented accommodation suits your plan. A single monthly payment alone does not answer this question. You need a common starting point, the same period under consideration and a clear separation between expenditures and assets that remain at the end. The following method is an editorial framework, not a finished buy-versus-rent calculator.
Start with the same housing service and the same assets
First describe which flats you are comparing and which differences you consciously accept. A small rental unit and a substantially larger owner-occupied home, without further explanation, address different housing questions. Also keep your existing starting assets the same in both variants.
If part of those assets is used for the purchase, it initially remains visible as existing assets on the rental side. Any assumed investment of those assets requires its own justified assumption. A secure high interest return must not simply be added to make a preferred variant win.
Keep payments and balances separate
On the purchase side are actual or explicitly assumed acquisition payments and ongoing ownership payments including the loan instalment. At the chosen end point the property value and outstanding debt are shown separately. On the rental side are rent payments and the remaining cash balance.
A repayment amount is initially part of an actual payment. Its effect on the final debt becomes visible in the balance. It is not also added as a further expense in addition to the full instalment. Nor is an assumed property value freely available cash as long as no corresponding sale takes place in the model.
A small invented end point
After the self-chosen period the purchase variant in the example would have a property with an assumed value of 300.000 Euro, an outstanding debt of 220.000 Euro and 10.000 Euro in cash. Without selling costs or taxes this arithmetically yields 90.000 Euro from property value minus debt plus cash. Under its own fully disclosed payment assumptions the rental variant would have a cash balance of 95.000 Euro.
The difference of 5,000 Euro is neither a recommendation to buy nor to rent. Even a different end value changes it. Moreover, the two end amounts alone do not yet explain which ongoing burden was required along the way and whether it could be borne.
Test the decision against its sensitive assumptions
Change holding period, major ownership expenditures, rent development and final property value one at a time. Mark each figure as an assumption in its own right rather than as a forecast. Individual additions are necessary for taxes, contracts, financing and, if applicable, selling costs.
A useful result states under which assumptions the evaluation flips and which housing needs the calculation does not express in euros. An apparently precise end amount without disclosed interim payments does not provide this decision aid.