Run a couple through a single-person calculator and both answers are wrong
Almost every retirement calculator assumes one age, one pot, one contribution, one date. Put each half of a couple through it separately and you get two answers that cannot both be right, because the two people are not independent. They share the spending, which is the input that dominates everything.
This calculator treats the household as it actually works: one target, funded by two pots, reached on one date, while keeping the ages and contributions separate, because those genuinely differ. The headline is the number of years until the combined pots reach the joint target, and the age each of you will be when that happens. An age gap does not change the date; it changes what the date means for each person, which is often where the real conversation starts. Underneath, three bars compare the joint timeline against what each of you would face alone, and that comparison is the most useful thing on the page, since it is the one no single-person calculator can produce.
Before leaning on any of it, know what shape of couple the model assumes: fully shared finances. Plenty of couples do not organise money that way, with separate accounts, unequal contributions, children from a previous relationship, or a prenuptial arrangement, and if your finances are genuinely separate, two individual projections with an agreed spending split is more honest than this model.
The invisible subsidy
Two people living together do not spend twice what one person spends. They spend somewhere between 60% and 75% of it. Rent or a mortgage barely changes. Council tax gets a 25% single-person discount, not a 50% one. Heating a house costs almost the same whether one or two people live in it, and broadband, standing charges and insurance are effectively fixed.
That is why the calculator has a solo spending share slider rather than assuming half. Set it to 65% and each of you alone would need 65% of the joint target, not 50%, which is why the solo bars run so much longer than intuition suggests. Most households land between 60% and 75%; set it against your actual fixed costs, and use the higher end if housing and bills dominate your spending.
The practical consequence is blunt. For most couples, sharing costs is worth more to the retirement date than either salary is. It is an enormous, invisible subsidy, and it is also why separation is financially devastating in a way that goes well beyond splitting the assets. Which is exactly why the solo comparison should be read carefully: it is a thought experiment that assumes each of you keeps your own current savings and contributions, and after a real separation that is rarely how assets divide. It illustrates what shared costs are worth, not what any particular outcome would look like.
The tax system quietly helps the couple too. Two people each drawing a modest income usually pay less total tax than one person drawing double, because allowances and lower bands apply twice. Tax is not in these figures at all, so the joint result is, if anything, mildly pessimistic on that front. Which allowances double, and the conversations worth having before either of you opens a spreadsheet, are laid out in the couples guide.
When 41 meets 38
Reaching the number together does not mean stopping together.
If one of you is 41 and the other 38, the older partner hits pension access three years sooner. That can be useful, since an unlocked pension shortens the bridge for the household, but it also means the younger partner may face years where their own money is locked while the household draws on the older partner's pot and accessible savings. This calculator deliberately does not model that interaction: the joint pot is treated as spendable on the FIRE date, which is not true when a large share sits in pensions. Run the joint date here first, then take it into the pension bridge calculator with your accessible and locked pots split out. For the target itself, counting both pensions together is right, if you share finances; for when you can actually spend them, it never is.
Age gaps also stretch the planning horizon. A couple five years apart needs the money to last longer than either would alone, because the younger partner outlives the joint retirement start by more years, and a longer joint horizon arguably justifies a lower withdrawal rate than a single 30-year retirement would; this tool applies one rate to both. The rich, broke or dead tool frames that trade-off directly.
The unequal middle of real careers
Contributions here are flat and permanent, and real careers are neither. Parental leave, part-time years, caring responsibilities and redundancy all interrupt saving, and they fall unequally, overwhelmingly on one partner in practice. A projection assuming both people contribute steadily for twenty years will flatter most households, so if one of you is likely to step back for a stretch, rerun the plan with that partner's contributions reduced and see what the date does.
What if only one of you wants to retire early? Common, and the tool still helps: reaching the joint number means the household could stop, and if one partner keeps working, their income reduces the drawdown and extends the pot considerably. Lowering joint spending by their after-tax earnings approximates it well. Larger households than two are out of scope, though totalling the extra savings and contributions into one combined partner gets you a serviceable answer.
Returns are constant here, as everywhere on this site; for the effect of an uneven sequence, use the Monte Carlo simulator. And household finances involving pensions, tax and two people's circumstances are exactly the situation where a qualified adviser is worth the fee; the FCA's consumer pages are the place to check anyone you consider.