# Tracking a mortgage > Dutch mortgages are usually several loan parts with different types, rates and end dates. Gylder models them as parts, so the schedule, the interest split and extra repayments all behave the way your lender does. A Dutch mortgage is rarely one loan. It is commonly split into **parts**, each with its own type, rate, term and tax treatment, which is why a single balance and a single rate cannot describe it. Gylder models parts directly. You can add as many as your contract has, and everything downstream, the schedule, the monthly split, the payoff date, is computed from them together. ## Setting one up A mortgage attaches to a property, so add it from the house. Per part you give: - **Type**: annuity (annuïteit), linear (lineair) or interest-only (aflossingsvrij) - **Sum at the start**: the original principal on your contract - **Current balance**: from your latest statement - **Total term**: what you signed for, usually 30 years - **Interest rate** Both the original principal and the current balance are asked for on purpose. The first anchors the schedule, the second anchors reality. Optionally, per mortgage: **NHG**, the **fixed-rate end date**, the **boetevrij** allowance, and whether the interest is **tax-deductible** (hypotheekrenteaftrek). As you type, a preview shows the approximate monthly payment, the year it pays off, and how much of the principal you have already repaid. ## Why your balance and the schedule are reconciled An amortisation schedule computed from the original principal, rate and term will rarely land exactly on the balance your bank shows today. Overpayments, payment dates, rounding and rate changes all pull it around. Rather than silently trusting the formula and showing you a balance your bank disagrees with, Gylder reconciles the difference at the start and records it as a **one-time adjustment**, which is noted on the property page. That is why the day-one paid-off percentage is anchored to the balance you stated rather than to what the maths alone would produce. Your number, not ours. ## Loan part types **Annuity** keeps the monthly payment level. Early on most of it is interest and little is principal; the mix shifts over time. **Linear** repays the same amount of principal every month, so the total payment starts higher and falls as interest shrinks. **Interest-only** repays no principal at all. The balance stays where it is until the term ends, which is what makes the payoff date on an interest-only part meaningful in a different way from the others. Mixing types across parts is normal, and it is exactly why the parts model exists. ## Extra repayments Log one with **Extra repayment**. It is recorded as an event on a specific part, and balances and the schedule recompute from your full event log rather than being edited in place. Four things it asks, and each changes the outcome: **Which part.** The interface notes that paying down the higher-rate part saves more interest, which follows from the arithmetic of interest. **The effect.** Either **lower monthly** with the term unchanged, or **shorter term** with the monthly unchanged. This mirrors the choice your lender gives you, and you should record what you actually chose rather than what you would prefer. **Whether it is already in your balance.** The important one, and easy to get wrong. If you are itemising a payment that was already included in the balance you entered, choose **already in my balance** and your stated balance stays put. If you forgot to log it and your balance should drop, choose **new info**. Getting this backwards double-counts the repayment or loses it. **Penalty-free allowance.** Gylder tracks how much of your boetevrij allowance remains this year, typically 10% of the original sum on a fixed-rate part and 100% on a variable one. Exceed it and it warns that the lender will charge boeterente on the excess, with an estimate based on today's market rate for the remaining fixed period. It is an estimate for orientation. Your lender's own calculation is the one that will be charged. Logged repayments can be edited or deleted afterwards, and the balance recomputes each time. ## Bouwdepot If you took a renovation escrow, add it to the mortgage: the initial deposit, the expiry date, and the interest the bank pays on the balance held. Drawdowns are logged as you spend, each with an amount, a date and a description such as `Kitchen renovation` or `Solar panels`. Gylder shows how much has been drawn, what remains, and how long until it expires, counted in days as the deadline approaches. Unused bouwdepot money is usually applied against the mortgage at expiry, so the countdown is worth watching. ## Closing a part, versus deleting it These are different actions and the difference matters. **Close part** marks a part as finished and keeps it for history. Use it when a part is genuinely over: refinanced, paid off, or the house was sold. Closed parts stay visible under closed loan parts, so your past remains explicable. **Delete part** removes it entirely, and exists only to fix a setup mistake, such as entering the same part twice. Deleting a part that really existed erases history that your balance depends on. If in doubt, close rather than delete. ## What Gylder does not do It does not advise. The LTV flag and the higher-rate hint on repayments are observations that follow from the numbers, not recommendations to refinance or overpay. It does not model your tax return. Marking a part tax-deductible records that the interest is deductible under hypotheekrenteaftrek so the figure can be shown; it is not a calculation of what you will get back. It does not know about changes you have not entered. A rate that ends its fixed period, a lender switch, or a new part all need entering, because nothing here is connected to your lender.