Nobody moves back because of the tax rate. They move back because of the school run.

Every family arrives with a spreadsheet. It is usually a good spreadsheet. It has tax rates, residence requirements, visa timelines, and often a column lifted from a published country ranking. It is also, almost without exception, a spreadsheet about the wrong half of the decision.

Nobody has ever moved home because the corporate rate went up two points. They move home because the school run takes ninety minutes each way, because the spouse has spent eight months without a single friend, or because the town they fell in love with in August turns out to be shut from November to March.

There are two decisions here, and they get mistaken for one.

The country decision is legal. The city decision is domestic.

The country decision is answerable at a desk. Can we get in, what does it cost us in tax, how long until we are secure, what does leaving trigger. It is written down. It is checkable. It is mostly public. It is the decision that is easy to get right — and the one everybody spends their energy on.

The city decision is answerable only by living. It has no statute and no index worth the name. It is also the decision that determines whether you are still there in three years.

Here is the method, in order.

One: gates before scores

The most common error in a relocation spreadsheet is scoring something that should be a gate.

A gate is binary. Fail it and the country leaves the list — no amount of sunshine, yield or headline tax rate compensates. Score your gates instead of applying them and you end up with a beautifully ranked list of countries you cannot move to.

The country gates:

• Does the programme accept your nationality at all. Several do not, and the restriction is rarely on the brochure.
• Are you permitted two citizenships — at both ends. Some countries require you to renounce on naturalisation. Some countries you are leaving take it badly.
• How many days a year must you physically be present. This is the number that quietly decides whether the plan is a life or a fiction.
• Conscription exposure for sons. Nobody puts this in the spreadsheet. Several otherwise excellent destinations acquire a claim on your teenage children.
• The language or civics requirement at naturalisation — and whether accommodations exist if someone in the family needs one. Establish this in year one, not year five.
• What the country you are leaving charges you for leaving. Exit taxes fire on departure, not on arrival, and there is no fixing them afterwards.

Only the survivors get scored. Usually that is four or five countries, not thirty.

Two: score the country only on what is genuinely national

This is the rule that saves the most wasted work.

Score each thing at the level at which it is decided. A national cost-of-living figure for a country with one expensive capital and eleven cheap provinces is not a fact about anywhere you are going to live.

Three: know what the rankings are actually made of

Every country index you have read — liveability, prosperity, quality of life, best places to move — is assembled from the same short shelf of public datasets.

Rule of law, corruption and political stability come from the World Bank's governance indicators. Life expectancy, health spending and air quality come from the WHO. Education comes from the OECD's PISA rounds. Income, prices and purchasing power come from the World Bank and the IMF. Tax comes from the OECD's tax database and the national authorities. Homicide comes from the UN. These are serious, comparable, slow-moving series, and they are free to anybody.

Everything softer than that is one of two things. Either it is crowd-sourced — a self-selected panel typing in what they pay for a flat and how safe they feel, which is genuinely useful for order of magnitude and useless as a basis for a decision — or it is a proprietary basket built for corporate assignees, priced around international-school fees, secure housing and a car with a driver. Those numbers are real. The question they answer is what should we pay a posted executive, which is not your question.

Here is the part the rankings do not advertise. The data is common property. The ranking is the weighting. Everyone is drawing from the same wells; what differs is how much weight each publisher puts on safety versus climate versus healthcare versus tax. Change the weights and the winner changes. A published index therefore tells you the priorities of the people who published it, and nothing whatsoever about yours.

My view: the most useful thing you can do with a country index is read its methodology page and then never look at the table.

Four: write your own weights down before you look at a single country

Do it first, in writing, and date it. Otherwise you will discover your weights retroactively, in the shape of whichever country you had already fallen for.

No published ranking is weighted like any of those rows, because it cannot be. It has to be weighted for everybody, which means it is weighted for nobody.

Five: the city — where the moves actually fail

Take the surviving countries and name three to five candidate cities in each. Then stop thinking about cities and drop to districts. In a great many perfectly good cities the honest question is not whether to move there, but which four neighbourhoods are the answer — and cost, safety and schools all resolve at that level, not the city's.

The city gates:

• Regional tax. In Spain, wealth and inheritance charges differ sharply by autonomous community. In Switzerland the arrangement is agreed with a canton, not with the country. The region can undo the country's headline in either direction.
• A school with a place in your child's year. Not "there are international schools here". A place. Waiting lists at the good ones run a year or two, and admission — not fees — is the binding constraint.
• The specific medical thing, if your family has one. It reduces most countries to two or three cities in an afternoon.
• One flight to the anchor — parents, the business, a child at university. A connection turns monthly into quarterly, and quarterly into estrangement.
• The time zone, against whoever pays you.

Then score, in this order, because this is the order in which families actually break.

1. The school run. Ninety minutes a day in traffic, twice, is the most reliable predictor of a family going home that I know. People model the house, and they model the school, and they never once model the road between them at eight in the morning.
2. The district. Everything domestic resolves here. A city-level crime number is an average of places you would live and places you never would.
3. Whether the spouse has something to do. Work, a practice, a studio, a language course, anything. The trailing partner with no occupation and no friends is the most common single cause of a reversed move, and it appears in nobody's spreadsheet because it is nobody's line item.
4. Whether you can actually sign a lease. A foreigner with no local credit history meets a guarantor requirement in France, a payslip requirement in Spain, a co-signer and a stack of post-dated cheques elsewhere. This stops more arrivals in week two than any visa rule.
5. Seasonality. The seaside town you saw in August is a different town in November: restaurants shut, friends gone, one supermarket open.
6. The cost of entering. Deposits, furniture, a car, registration fees, the temporary flat before the real one. It is a serious sum on top of the rent, and it is almost never budgeted.
7. How fast you could leave. Nobody wants to think about it in month one. It is the cheapest insurance in the exercise.

The three tests nobody runs

Live there in the worst month. Not August. Four to six weeks in the month the locals complain about — the wet one, the dark one, the empty one. If it still works then, it works.

Get the school place in writing before you sign a lease. Visit, meet the head, ask for the actual availability in that year group. A verbal "we usually have room" is not a place.

Book a real appointment with a real doctor in the system you will actually use, and see how long it takes and what a foreigner is charged. Before you commit, not after.

Then rent for a year. Buying in the first year is the most expensive available method of discovering you picked the wrong district.

The order, on one page

1. Write your weights down, and date them.
2. Apply the country gates. Most of the list disappears here.
3. Score the survivors only on what is genuinely national — tax, immigration, stability, treaties. Our country guides and programme index exist for this stage, and the Arrive Index does the scoring with its weights on the table — including a version you can re-weight for your own household.
4. Choose three to five cities, then drop straight to two or three districts and do the remaining work there.
5. Verify the two things no index can score: a school place and a medical appointment.
6. Live through the worst month.
7. Rent for twelve months.
8. Only then buy anything.

Verdict

Spend your analysis on the country and your time on the city. The country decision is public, checkable and forgiving of research: you can get it right from a desk in a few weeks, and a good adviser gets it right faster. The city decision cannot be researched to a conclusion. It can only be tested — and the families who test it, in the wrong month, with the school confirmed and the lease short, are the ones still there in five years.

The tax rate is the part of the move most likely to be correct. The school run is the part most likely to end it.