Buying a home is exciting, but the process can be difficult to follow especially when you haven't done it before. Estate agents talk about offers, closing dates, chains and completion. Lenders talk about affordability, credit commitments and criteria. Solicitors talk about searches, titles, contracts and settlement. Surveyors talk about condition, valuation and defects, and the list goes on.

Everyone seems to know their part and you are expected to understand all of it. One of the most common mistakes buyers make is starting with the property. You see a house or flat in your favourite area. You imagine where your furniture will go, or having a cuppa at the kitchen window. And before long, you are emotionally invested. But the figures, documents and possible risks haven't yet been checked and this where things could go wrong. It is better to understand your position first before getting emotionally invested. That means looking at your income, deposit, debts, credit history and likely mortgage options. You should also have your paperwork ready and know which professionals you will use.

This guide covers the main points first-time buyers and home movers should think about before committing to a purchase. The process differs across the UK. Some sections relate mainly to Scotland, while others apply to England and Wales. These differences are flagged where needed.

1. Start with purchasing power, not the property

Your purchasing power is not just your salary multiplied by a number. A lender will look at how your income is earned, what debts and regular commitments you have, the size of your deposit and your credit history. They will assess the property too. Two buyers earning the same amount can receive very different mortgage outcomes. One may have low debt, stable employment and a large deposit. Another may have childcare costs, credit card balances, car finance and a recent missed payment. Their incomes may be the same. Their borrowing positions are not. Before making serious offers, you should understand:

You also need to factor in legal fees, surveys, removals, insurance and any work needed after you move in. An agreement in principle is normally a sensible starting point.

It gives an early indication of how much you may be able to borrow based on the information available at the time. It may help identify suitable lenders and bring possible problems to the surface. Just keep in mind, this is not a mortgage offer, the lender still needs to check the documents, complete its underwriting and approve the property to get at that stage.

2. How lenders assess employed income

Lenders want to know how much you earn, where the income comes from and whether it is likely to continue. If you are employed, they will usually start with your basic salary. You may be asked for recent payslips, bank statements, a P60 or your employment contract, sometimes even a reference. Overtime, commission, bonuses and allowances may be considered and the amount accepted varies between lenders. One lender may use an average while others may cap it at set level. Some want to see that it has been received regularly for several months, or even longer. And here is an example, someone earning a basic salary of £35,000 plus regular overtime may receive different borrowing figures from different lenders.

A lender may accept most of the overtime when there is a clear history. Another may take a just the salary even if there is a long track record available. This is why checking first will make your life easier later on.

Recent job changes

Changing jobs does not automatically stop you from getting a mortgage.

Some lenders will consider an applicant who has recently started a new role, especially where they are doing similar work for a new employer. Others may want you to have passed probation or completed a set period in the role. Your wider employment history matters too so you need to be prepared to answer additional questions about that.

Some lenders may want around 12 months of work history, depending on the circumstances and the rest of the application. Do not assume that a signed contract or completed probation will satisfy every lender. Check your position before committing to a purchase.

3. Self-employed income and company directors

Self-employed income is one of the areas where lender criteria can vary most. Clients who are limited company directors sometimes assume they will be treated as employed because they get paid through payroll. However, if you own a significant share of the business, (25% or more) many lenders will see you as self-employed and company's performance will need to be assessed. Typically this means reviewing not just your payslips but also accounts, profits, dividends, and whether the income being taken from the business appears sustainable. This can easily create pitfalls.

For example, if dividends are higher than the company's net profit, or the business has had a sudden increase in profitability, a lender may ask more questions. Different lenders assess self-employed income in different ways. Some work from the latest year's income, others average the last two. Some look at salary and dividends while others consider net profit (share of) plus salary. The position can also differ depending on whether you are a sole trader, limited company director, contractor, CIS worker or partner in a business.

Common documents may include tax calculations, Tax Year Overviews, company accounts, business bank statements, personal bank statements, accountant's details or an accountant's certificate, and evidence of contracts or future work where relevant.

A broker can be particularly useful here because the question is not simply, "How much did you earn?" It is, "Which lender will understand how that income is generated, evidenced and sustained?"

4. Benefits, pensions, maintenance and other income

Some lenders accept income from sources outside employment or self-employment.

This may include:

The rules vary between lenders. Some may use the full amount, others accept only part of it or exclude it completely. The lender may look at how long the income has been received and whether it is expected to continue. Income linked to a child may only be accepted until the child reaches a certain age. Maintenance may need to be supported by a court order, written agreement or clear payment history. Evidence may include award letters, pension statements, bank statements and maintenance agreements. An income type being rejected by one lender does not mean it will be rejected by all lenders. It needs to be checked before the application is submitted.

5. What you owe affects what you can borrow

Most buyers have some form of financial commitment. The question is how they are going to affect your borrowing capacity and how they are being managed. Lenders will usually look to deduct them when assessing what you can borrow which can significantly reduce your borrowing.

However, the position can change if some of those commitments are due to be repaid before, or on, completion. Some lenders will disregard a debt that is being cleared, but this needs to be discussed and evidenced properly. For example, the lender may want to understand whether the repayment is coming from savings, sale proceeds, a gifted deposit arrangement or another acceptable source. This is why it is important to cover debts in detail with your broker early on. Whether a commitment is staying, being reduced or being cleared can make a meaningful difference to your maximum borrowing.

The same applies in reverse. If you take on new debt after an initial agreement in principle, such as new car finance or a personal loan, the original figures may no longer be accurate. A decision in principle is only based on the information available at the time, so any change in debt can affect the final mortgage outcome.

Debt-to-income ratios

Some lenders look closely at how much debt you have compared to your income. This is called a debt-to-income ratio. If your credit cards, loans and finance agreements are high relative to your income, it can restrict your options. Even if payments are up to date, the lender may see the overall debt level as a risk. It is not always about whether you can afford the minimum payments. It is about whether the lender feels the total position is sustainable alongside the new mortgage.

If you are thinking about buying a car, taking finance, consolidating debt or using a credit card before applying for a mortgage, speak with a broker first. A new commitment can reduce what you can borrow. Do not assume a lender will ignore a debt just because you intend to repay it later.

Avoid taking new credit

An agreement in principle is based on the information available on the day it is completed. Taking new credit can change the result. A personal loan, car finance agreement or increased credit card balance may reduce your maximum borrowing. Lenders may complete another credit search before issuing the offer or before completion. Speak with your adviser before applying for new credit during the mortgage process.

6. Credit problems do not all mean the same thing

Bad credit is not one single category. A missed mobile phone payment from two years ago is not the same as a recent default, a debt management plan, an IVA or bankruptcy. Lenders look at the type of issue, the amount, the date, whether it has been satisfied, and the reason behind it.

The more recent and serious the issue, the more likely it is to affect lender choice, deposit requirements, interest rate, loan size and LTV. But credit issues do not always mean the door is closed.

The important thing is disclosure. A broker cannot place a case properly if the credit position is only discovered after an application has been submitted. Being upfront about credit issues from the start does not automatically mean a case cannot proceed. In many situations, it simply means the case needs to be placed with the right lender and packaged correctly.

What can help if you have impaired credit?

Allow the broker to match the case to lenders who are more likely to consider it. A clear explanation does not erase credit history, but it can help the case make sense. For example, a lender may view a one-off issue caused by redundancy, illness or separation differently from repeated missed payments with no clear explanation. There are no guarantees, but context matters.

7. Prepare your documents before you are under pressure

A mortgage application usually moves more smoothly when the documents are ready and consistent. The lender will check whether the information on the application matches the evidence. Your income should match the application. Your bank statements should show the income being received. Your deposit should be traceable. Your address history should line up. Any large payments may need explaining.

The exact documents needed will depend on your circumstances. An employed applicant, a self-employed applicant, a company director, a buyer using a gifted deposit and someone buying a leasehold property may all need slightly different evidence. For example, leasehold properties will require information on lease length, ground rent, service charges, buildings insurance, management company details, planned major works and restrictions within the lease. For Scottish flats or factored properties, your solicitor may need to review title deeds, factoring information, buildings insurance, common repairs and any planned works.

Gifted deposits

For gifted deposits, lenders and solicitors will need to understand who is gifting the money, where the funds came from and whether it is genuinely a gift rather than a loan. One of the most common causes of delay is not the lender being difficult. It is the application being submitted before the evidence is ready. That is why we ask for the basics at decision in principle stage. It helps us understand your position properly from the outset, identify what may be needed later, and highlight anything that could raise questions before you are under pressure to move quickly. Make sure you have the following information ready:

8. The property

When you buy a property with a mortgage, the lender is not just assessing you. They are also assessing the property. The property is the lender's security. If the lender does not like it, the mortgage may not proceed, even if your income and credit are strong.

Things to watch include:

The list is not exhaustive. A beautiful property can still be a difficult mortgage case. This is why it is risky to commit emotionally or financially before understanding whether the property fits lender appetite.

9. Leasehold properties

This section is mainly relevant to England and Wales, where flats are commonly leasehold and some houses may also be leasehold. Leasehold means you own the right to occupy the property for the remaining term of the lease, rather than owning the land outright in the same way as a freehold property. That does not automatically make the property unsuitable, but the detail matters.

Lenders, solicitors and buyers will usually want to understand how many years are left on the lease, how much the ground rent is, whether it increases over time, how often it is reviewed, and whether the terms could be considered onerous. They will also want to understand the service charge position, whether the charge is reasonable for the building, whether major works are planned, whether the building is properly insured, and whether there are any restrictions, cladding or fire safety concerns, management issues or lease terms that could affect the lender's requirements.

Lease length can materially affect mortgageability and future saleability. A short lease can reduce the value of the property and may make some lenders uncomfortable. Different lenders have different requirements, but many will want a certain number of years remaining at the start of the mortgage and enough years left at the end of the mortgage term.

A flat with 95 years remaining may be viewed very differently from a flat with 68 years remaining. Short leases can often be extended, but that can involve cost, time, valuation advice and legal work, all of which affect overall mortgageability. It is not something to discover late in the process. If you are buying a leasehold flat, ask about the lease length before you get too far.

Ground rent is another area to check carefully. The issue is not only the amount payable today, but whether it increases in the future and how that increase is calculated. A ground rent that looks manageable at the start may become a problem if it doubles at set intervals, increases too frequently or is written in a way that a lender considers onerous.

Service charges also matter. A service charge is common with flats and managed developments, and it is not automatically a problem. The question is whether the charge is reasonable, affordable and properly managed. A very high service charge can affect your own monthly budget and may also make the property less attractive to future buyers. A very low service charge is not always a positive either, because it may mean the building is not being properly maintained and larger repair bills could follow later.

Before buying a leasehold property, you should try to understand what the service charge covers, whether there is a reserve or sinking fund, whether major works are planned, whether there have been disputes with the freeholder or management company, and whether there are any unpaid charges linked to the property.

This is where your solicitor's role is important. They will review the lease, the management pack and the legal structure. Your broker will also need to know if there are any lease terms, ground rent clauses or service charge concerns that may affect the lender's appetite.

This is Part 1 of a two-part guide. Part 2, under the same title, will follow in a couple of weeks.

Your home may be repossessed if you do not keep up repayments on a mortgage secured on it.