You want a thorough retirement model. Boldin is the most thorough in the US. Delphina is the most useful in the UK. Here is where the two diverge.
Boldin (formerly NewRetirement) lets you model retirement at a level of detail that no UK tool matches. You can enter 30+ spending categories, year-by-year changes to those categories, planned one-off expenses (a kitchen renovation at 62, a grandchild's education at 70), multiple income sources, social security timing, Medicare premiums, and long-term care costs. The platform then runs thousands of Monte Carlo simulations and tells you the probability of success under each scenario.
For a US household with a clear picture of their retirement spending and a willingness to spend 2-3 hours on the input form, Boldin gives the most comprehensive consumer-facing planning available. The healthcare cost modelling in particular is meaningfully better than anything else at this price point.
Delphina plans from your real money. You add your UK bank, pension and ISA balances, and the platform does not need a 30-field form. The 4% safe withdrawal rate, the UK State Pension forecast, the pension tax-free lump sum, the annual allowance taper, and the dividend and capital gains allowances are all modelled automatically.
Delphina also updates the plan as your life changes. A pay rise, a bonus paid into a SIPP, a redundancy payout, a sabbatical: the projection shifts in real time. Boldin's model is a snapshot. Delphina's is a living model.
Boldin's US-specific tax modelling is genuinely better than Delphina's for US households. Roth conversions, Social Security claiming strategies, and Medicare premium cliffs are all modelled with detail. The platform is built for the US tax code.
Delphina is built for the UK. If your accounts are UK-based and your planning question is in years not decades, Delphina gives you a useful answer in 10 minutes rather than 3 hours. If your situation is genuinely complex, Boldin's depth wins for US households. For UK households the depth is in the wrong place because the tax rules are different.
Pull your State Pension forecast from gov.uk and your latest workplace pension statement. Connect both to Delphina this week. The 20-minute setup will give you a specific number for your retirement gap, and one monthly action to take before the end of the month.