What Is Burden Sharing? Definition & 2025 Spending Data

Burden sharing is the principle that allied nations should split the costs of collective defense fairly, rather than let a few members carry a disproportionate load. There's no single global "burden sharing score" — it's measured relative to a baseline, and the broadest baseline available is world military spending itself: $2,740.0bn in 2025, our calculation from SIPRI country-level data covering 149 countries.

01 What Does Burden Sharing Mean?

In defense policy, burden sharing describes how the cost of a shared security commitment is distributed among the parties that benefit from it. The term is used most often inside alliances, where members pool military capability and expect participation to be roughly proportional to size, wealth, or the risk each member faces — rather than a small number of states effectively subsidizing the rest.

The concept itself is descriptive, not a verdict. It names a comparison — one country's spending against another's, or against an alliance total — without saying in advance who is or isn't "pulling their weight." That judgment depends on which metric is used and what baseline it's measured against.

02 How Burden Sharing Is Measured

Burden-sharing comparisons typically use one of three approaches:

• Spending as a share of GDP — the most common alliance benchmark, since it accounts for the fact that larger economies can spend more in absolute terms without stretching further.
• Spending as a share of an alliance or coalition total — a member's outlay measured against the combined spending of everyone in the group.
• Spending as a share of world military expenditure — a broader baseline, useful for placing any single country's effort in global context rather than just within its own alliance.

All three require a denominator. Without one, a raw dollar figure says little about whether a country's contribution is large or small relative to its means or its peers.

03 The 2025 World Total: A Baseline for Comparison

For 2025, summing SIPRI's country-level military expenditure data across the 149 countries it reports produces a world total of $2,740.0bn, expressed in constant 2024 US dollars. This is our own calculation from SIPRI's country data, not a figure SIPRI itself publishes as a headline total.

That total is the widest denominator available for a burden-sharing comparison. The mechanic is simple: divide a country's or alliance's spending by the world total to get its share of global military expenditure. Narrower comparisons (a country against its alliance, rather than against the whole world) use a smaller, alliance-specific denominator instead, which SIPRI's country series don't directly provide as a summed figure.

04 Burden Sharing in NATO and Other Alliances

NATO is the most visible arena for burden-sharing debate, since it publishes its own defense-spending guideline for members and regularly compares national outlays against it. The same logic — comparing a member's spending to a shared benchmark — applies to any formal alliance or informal coalition, not just NATO. What changes between alliances is the denominator: NATO burden-sharing figures are measured against NATO's own combined total, which is a subset of the $2,740.0bn world figure, not the same number.

Because the world total in this dataset covers all 149 reporting countries — allied and non-allied alike — it isn't itself a NATO or alliance-specific burden-sharing metric. It's the outer boundary: the full pool of global military spending that any narrower alliance share is drawn from.

05 Limitations of Burden-Sharing Comparisons

Burden-sharing figures are only as complete as the underlying data. The 149-country total used here is a floor, not a full accounting of world military spending.

Comparisons built on GDP shares or alliance totals carry their own limits too: GDP-based figures can shift year to year with exchange-rate and price effects even when real spending is flat, and alliance totals depend on which members are counted and when they joined. None of these limitations invalidate the concept of burden sharing — they just mean any single percentage should be read alongside its denominator and its data source.

06 Where to See Country-by-Country Shares

Defining burden sharing in the abstract only goes so far — the practical question is usually which countries spend how much, relative to what. The 2025 world rankings break the $2,740.0bn total down by country, so individual shares can be checked directly rather than taken on faith. For definitions of related terms used alongside burden sharing, see the glossary.