# Premium growth metrics: reading GWP, NWP and retention like an analyst
A mid-size US commercial carrier reports 18% premium growth for the year. Investors cheer. Then the reinsurance disclosure shows the carrier ceded 40% more premium to reinsurers than the prior year, retention fell five points, and net income barely moved. The "growth" was mostly gross inflation passed straight through to reinsurers. This is the single most common trap in reading insurer top-line numbers, and this lesson gives you the tools to avoid it.
Gross Written Premium (GWP): the total premium an insurer books on policies during a period, before any reinsurance is subtracted. This is the "headline" growth number companies like to lead with.
Ceded premium: the portion of GWP an insurer pays to a reinsurer (a company that insures insurers, spreading catastrophic or concentrated risk) in exchange for the reinsurer taking on part of the liability.
Net Written Premium (NWP): GWP minus ceded premium. This is what the insurer actually keeps exposure to, and it's a better proxy for real economic growth.
Retention ratio: NWP ÷ GWP. It tells you what share of business the insurer keeps on its own book versus passing to reinsurers.
Renewal ratio (or retention rate on policies): the percentage of expiring policies that renew with the same carrier. Don't confuse this with the premium retention ratio above; it's a policy-count or policy-premium metric measuring customer stickiness, not reinsurance structure.
GWP growth driven by rate increases (raising prices on existing risk) is different from GWP growth driven by new business volume, and both are different again from growth that simply reflects the carrier ceding less to reinsurers than before (which inflates NWP growth without any real expansion).
A carrer can show:
This last pattern is exactly what happened across parts of the US property catastrophe market around 2023-2024, when reinsurance rates spiked after major hurricane losses, promptingpromptingPrompt engineering is the practice of designing and refining text inputs to guide large language models toward accurate, relevant, and reliable outputs.View full definition → some primary insurers to retain more risk rather than pay up for cessions (a pattern widely discussed in reinsurance renewal commentary from brokers like Guy Carpenter and Aon).
Take a hypothetical mid-size US commercial lines carrier, "Meridian Insurance" (illustrative, not a real company).
| Year | GWP ($M) | Ceded Premium ($M) | NWP ($M) | Retention Ratio |
|------|----------|---------------------|----------|------------------|
| Y1 | 1,000 | 250 | 750 | 75.0% |
| Y2 | 1,100 | 275 | 825 | 75.0% |
| Y3 | 1,250 | 400 | 850 | 68.0% |
| Y4 | 1,450 | 500 | 950 | 65.5% |
| Y5 | 1,700 | 550 | 1,150 | 67.6% |
GWP growth Y1 to Y5: (1,700, 1,000) / 1,000 = 70%.
NWP growth Y1 to Y5: (1,150, 750) / 750 = 53.3%.
The gap (70% vs 53.3%) tells you that roughly a quarter of the apparent growth story is reinsurance structure, not net economic expansion. An analyst reading only the GWP headline would overstate the company's real risk-taking and earnings power by a wide margin.
Quick calculation to try yourself: if a carrier's GWP grows from $500M to $600M (20% growth) and its retention ratio drops from 80% to 70%, what's the NWP growth?
A 20% GWP headline becomes 5% real net growth once you adjust for retention. This is the calculation every insurance equity analyst runs before believing a growth story.
These are estimates and vary significantly by line of business (personal auto behaves very differently from cyber or catastrophe property), so always check the specific segment.
Public insurers disclose GWP, NWP, and retention in 10-K filings (annual reports filed with the US SEC) and in quarterly earnings supplements. European insurers disclose comparable figures in SFCR reports and IFRS 17 segment disclosures. A useful free primer on how premium flows through an income statement is the NAIC's consumer-facing glossary.
Knowledge check
1. A carrier reports strong GWP growth, but its retention ratio (NWP/GWP) falls sharply during the same period. What does this combination most likely indicate?
2. Why is Net Written Premium (NWP) generally considered a better proxy for an insurer's real economic growth than Gross Written Premium (GWP)?
3. An analyst wants to know whether customers are staying loyal to a carrier, independent of how much risk the carrier cedes to reinsurers. Which metric should they look at?
4. Select ALL correct answers describing scenarios that would make headline GWP growth misleading as a signal of real business expansion.
Select all the correct answers.
5. Select ALL correct answers about the relationship between GWP, ceded premium, and NWP.
Select all the correct answers.
While retention ratio (NWP/GWP) is about reinsurance economics, renewal ratio is about whether customers stay. A property insurer might report:
Multiply these dynamics together and you can decompose GWP growth into: rate (price), retention (existing customers), and new business (fresh customers). This decomposition is standard in earnings calls for carriers like Progressive, Travelers, or Allianz, where management explicitly breaks out "rate" versus "exposure" versus "new business" contributions to premium growth. When rate is doing all the work and renewal ratio is falling, that's a warning sign: customers may be leaving faster than price increases are compensating, meaning future GWP growth is at risk.
1. Is the reported growth GWP or NWP? If GWP only, ask for the retention ratio.
2. Has the retention ratio moved more than 2-3 points year over year? If so, reinsurance strategy, not organic growth, may explain the headline.
3. Is growth coming from rate, retention, or new business? Rate-driven growth with falling renewal ratios is fragile.
4. For catastrophe-exposed lines, compare retention ratio trends against reinsurance market pricing cycles (hard market = carriers cede more or retain more depending on capital position and risk appetite).